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1983 Behavior of Euphorbia Heterophylla Seed Bank. Vernon B. Langston Louisiana State University and Agricultural & Mechanical College
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Recommended Citation Langston, Vernon B., "Behavior of Euphorbia Heterophylla Seed Bank." (1983). LSU Historical Dissertations and Theses. 3929. https://digitalcommons.lsu.edu/gradschool_disstheses/3929
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Langston, Vernon B.
BEHAVIOR OF EUPHORBIA HETEROPHYLLA SEED BANK
The Louisiana Staie University and Agricultural and Mechanical Ph.D. Col. 1983
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Copyright 1984 by Langston, Vernon B. All Rights Reserved
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University Microfilms international
BEHAVIOR OF EUPHORBIA HETEROPHYLLA SEED BANK
A Dissertation
Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy
in
The Department of Plant Pathology and Crop Physiology
by
Vernon B. Langston B.S., Mississippi State University, 1977 M.S., Mississippi State University, 1979 December, 1983 © 1984
VERNON B. LANGSTON
All Rights Reserved ACKNOWLEDGEMENTS
The author wishes to express his gratitude to the members of his
graduate committee, Dr. J. B. Baker, Dr. R. L. Chapman, Dr. L. M.
Kitchen, Dr. J. E. Sedberry, Jr., Dr. L. C. Standifer, Jr., and Dr.
K. W. Tipton for their advise and constructive criticism of the
manuscript.
The author is grateful to Dr. T. R. Harger, committee chairman,
for his guidance, assistance, and patience during the course of this
research. The educational opportunities and research funds provided
by the Department of Plant Pathology and Crop Physiology and the
Louisiana Soybean Promotion Board were greatly appreciated.
The author gratefully acknowledges the technical assistance of
Ms. Lydia Lyons, Ms. Nikki Seger, and Mr. Doug Goyer. Special
thanks are extended to fellow graduate students and research
associates, Scotty Crowder, Paulette Johnsey, Paul Nester, Robert
Prince, Jim Shrefler, Lee Godley, Barbara Hook, Joe David Smith,
Jeff Yoder, Phillip Barbour, and Scott Aison for their assistance
and encouragement.
Finally, the author wishes to dedicate this dissertation to his parents, the late Mr. Robert B. Langston, Jr. and his wife, Mrs.
Annie Jane Langston, and to his future wife Lydia L. Lyons, without whose continued support this endeavor would not have been possible.
ii TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS...... ii
LIST OF TABLES...... iv
LIST OF FIGURES...... vi
ABSTRACT...... vii
INTRODUCTION...... 1
LITERATURE REVIEW...... 3
MANUSCRIPT...... 26
LITERATURE CITED...... 68
Appendix 1 ...... 78
Appendix II...... 83
VITA...... 88
iii LIST OF TABLES
Table Page
Manuscript
1. Wild poinsettia seedling emergence during 1982 from seed buried in October 1981 as affected by burial depth.. 52
2. Wild poinsettia seedling emergence during 1983 from seed buried in October 1982 as affected by burial depth.. 53
3. Average maximum and minimum monthly air temperature for February through July in 1982 and 1983...... 54
4. Viability of wild poinsettia seed recovered after one or two years of burial at four depths...... 55
5. Emergence of an agricultural seed bank of wild poinsettia as affected by cultivation over a two year period...... 56
6. Number of viable wild poinsettia seeds in the 0 to 60 mm depth of soil as affected by different cultivation regimes and sampling dates...... 57
7. Number of viable wild poinsettia seeds in the 60 to 120 mm depth of soil as affected by different cultivation regimes and sampling dates...... 58
Appendix Table
Appendix I
1-1. Dry weight of wild poinsettia plants remaining in the soybean drill (150 mm on each side of the drill) after various weed-free maintenance periods in 1982 taken at harvest...... 79
1-2. Dry weight of wild poinsettia plants remaining in the soybean drill (150 mm on each side of the drill) after various weed-free maintenance periods in 1983 taken at harvest...... 80
1-3. Dry weight of wild poinsettia plants remaining in the middles after various weed-free maintenance periods in 1982 taken at harvest...... 81
iv Table Page
I-4. Dry weight of wild poinsettia plants remaining in the middles after various weed-free maintenance periods in 1983 taken at harvest...... 82
Appendix II
II-l. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for wild poinsettia density in the row...... 84
II-2. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for wild poinsettia density in the middle...... 85
II-3. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for standing biomass in the row...... 86
II-4. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for standing biomass in the middle...... 87
v LIST OF FIGURES
Figure Page
1. Daily precipitation and dates of major emergence flushes of wild poinsettia from the buried seed study for 1982 and 1983 growing seasons...... 61
2. Wild poinsettia density in the row as affected by planting dates (E = early, L = late), post-planting cultivations (IX = once, 2X = twice), and weed-free period taken at harvest (October 28, 1982 and October 6, 1983)...... 62
3. Wild poinsettia density in the middles as affected by planting dates (E = early, L = late), post-planting cultivations (IX = once, 2X = twice), and weed-free period taken at harvest (October 28, 1982 and October 6, 1983).... 63
4. Standing biomass in the row as affected by planting dates (E = early, L = late), post-planting cultivations (IX = once, 2X = twice), and weed-free period taken at harvest (October 28, 1982 and October 6, 1983)...... 64
5. Standing biomass in the middle as affected by planting dates (E = early, L = late), post-planting cultivations (IX = once, 2X = twice), and weed-free period taken at harvest (October 28, 1982 and October 6, 1983)...... 65
6. Yield in 1982 as affected by planting dates (EPD = early planting date and LPD = late planting date) and weed-free period...... 66
7. Yield in 1983 as affected by planting dates (EPD = early planting date and LPD = late planting date) and weed-free period...... 67 ABSTRACT
Short term burial of freshly harvested seed and soil
disturbances in agricultural populations of wild poinsettia
(Euphorbia heterophylla L.) indicated a very low carry over of seeds
into the second season after dissemination. After seeds were buried
at 10, 50, 100, and 200 mm in the fall; 4%, 81%, 30%, and 1%,
respectively, produced seedlings during the following growing
season, and only 3%, 1%, < 1%, and 3% of the seeds, respectively,
were viable after one year. Soil disturbances (tillage) did not
affect seedling recruitment or longevity of wild poinsettia seed.
Early planting dates (May 1) of soybeans required 6 weeks of weed-free maintenance to prevent serious reinfestation and
subsequent yield reductions in fields with a high agronomic seed
bank of wild poinsettia, whereas for late planting dates (June 10) 3 weeks of weed-free maintenance was required. No significant
difference in yield was detected between one or two cultivations for
either planting date.
vii INTRODUCTION
The continuing increase of wild poinsettia [Euphorbia heterophylla (L.) Jacq.] as a major weed pest in soybeans [Glycine max (L.) Merr.] in Louisiana poses a major problem for farmers and weed scientists (34, 56, 73). Sanders (73) listed wild poinsettia as one of the ten most troublesome weeds in Louisiana soybeans, as well as one of the most costly weeds, irrespective of crops.
Wild poinsettia has become a serious weed problem in soybeans due to the following factors:
1. Wild poinsettia causes serious yield losses in soybeans,
especially if left uncontrolled in the early weeks of
growth (34, 38).
2. After maturity the adult plants remain green in the crop
for 60-80 days (94).
3. Dense populations of this weed can decrease yield by
competition and by imparing crop harvest. When harvesting
is possible, the latex sap in the stems of the wild
poinsettia increases the moisture content of the soybeans
and causes dirt and trash to adhere to the soybean
resulting in decreased crop quality (56).
4. There is no herbicide program which gives complete or
consistent control.
5. Shoot regeneration potential of wild poinsettia is very
common after treatment with currently used postemergence
Bannon et al. (5) reported the longevity and field germination 2
of wild poinsettia at different depths under field conditions in
Louisiana for a nine month period, however emergence and longevity
over longer periods has not been investigated.
Earlier research in Louisiana has shown that early planting of
soybeans generally provided better control of wild poinsettia (34).
Research in South Carolina indicated that planting dates did not
affect the weed-free maintenance period required to prevent yield reduction of soybean by weeds other than wild poinsettia (53).
However, at one location, a five week period of weed-free maintenance was needed to prevent serious weed reinfestation of early planted soybean plots, but only a three week period of weed-free maintenance was needed for late planted plots. Maximum soybean yield occurred after a weed-free maintenance period of three weeks for both early and late planted plots. Research investigating the effect of soybean planting date on wild poinsettia emergence, competitiveness of the weed, and subsequent reduction in soybean yield has not been conducted.
The objectives of this research were: 1) to determine the viability and germination of wild poinsettia seeds buried at different depths over one and two year periods; 2) to determine the influence of different tillage treatments over a two year period on seedling recruitment and longevity of an agronomic seed bank of wild poinsettia; 3) to determine the influence of soybean planting date and post-planting cultivation on the length of the control period required to prevent weed reinfestation and yield reductions when soybeans are grown in fields with a high seed population of wild poinsettia. LITERATURE REVIEW
Seed longevity and seedling emergence. The longevity of weed seeds
following burial in the soil has been investigated for several plant
species. In 1879, Beal buried 23 plant species in sand in
unstoppered bottles. The latest report of this experiment showed
that moth mullein (Verbascum blattaria L.) with 20% germination was
the only species still viable after 90 yr. In 1902, Duvel initiated
a buried seed experiment with conditions closer to the normal
seed-soil environment. He buried 107 plant species in sterilized
soil in flower pots placed upright and covered with porous saucers.
Toole (87), reported that 36 of the original 107 species in Duvel’s
study had viable seed after 39 years. Although these two studies
formed the basis for future buried seed experiments, the conditions present were too artificial to be useful in determining the
longevity of weed seeds in soils subjected to agricultural practices
(24).
For the "ideal" buried seed experiment, the seeds need to be placed at specific depths without being enclosed in containers.
This presented problems in recovering the seed, but with the availability of corrosion-resistant mesh materials it became possible to contain the seeds and maintain them in intimate contact with the soil environment (49).
Waldron (90) was one of the first scientists to recognize the agronomic importance of emergence periodicity data. His study included the following weed species: shepherd's purse [Capsella 4
bursa-pastoris (L.) Medicus]; frenchweed (Thlapsi arvense L.); green
foxtail [Chaetochloa viridis (L.) Beauvois]; giant ragweed or
kinghead (Ambrosia trifida L.); wild buckwheat (Polygonum
convolvulus L.); and wild oats (Avena fatua L.). Frenchweed
seedlings emerged from a maximum depth of 5 cm. Maximum emergence
of great ragweed seedlings resulted from burial at 5 to 7.5 cm, with
some emergence from 13 cm. Wild buckwheat and wild oat seedlings
emerged even when buried as deep as 7.5 and 13 cm, respectively.
The longevity of frenchweed seeds was enhanced by burial at depths
of 7.5 cm or more.
Chancellor (20) measured the depth of germination of several weed species common to Oxford, England, on three different soil types. He carefully excavated the seedlings, measuring the distance from the seed (if present) or its point of attachment, to the point along the hypocotyl at the soil surface. The majority (98%) of all seedlings measured arose from depths of 0 to 7 cm, regardless of soil type. Chancellor (20) stated "that it appeared that small-seeded weeds emerged only from shallow depths while large-seeded weeds could germinate from greater depths if conditions were suitable."
Banting (7), reported that the viability of wild oat seeds buried at depths from 0 to 25 cm was 26% and 0.64% of the original viabile seeds when buried for 12 and 80 months, respectively. The highest loss in viability occurred in the 0 to 5 cm layer, possibly due to the more favorable germination conditions. In long term studies he found that the loss of viability occurred in two phases, 5
a rapid loss within the first 2 years, followed by a slow decline
over a 6 year period.
Taylorson (84) indicated that there were marked differences in
loss of apparent viability when dormant and nondormant seeds of the
same species were compared in buried seed experiments located at
Beltsville, Maryland. He defined nondormant seeds as seeds that
germinated in the dark at one or more temperatures, with adequate moisture and air as the only other requirements; whereas, a dormant
seed was defined as requiring something in addition to these factors
to promote germination. The three weed species in this study were redroot pigweed (Amaranthus retroflexus L.), yellow rocket (Barbarea vulgaris R. Br.), and barnyardgrass [Echinochloa crus-galli (L.)
Beauv.]. Taylorson (84) stated "that the relative degree of initial
seed dormancy might be as important as the species itself in determining loss of viability (longevity) of weed seeds in soils."
He observed that dormant seeds maintained viability longer than nondormant seeds, and shallowly placed seeds lost viability faster than seeds placed at 15 cm.
Taylorson (85) also found that greater burial depth tends to maintain seed viability longer for common chickweed [Stellaria media
(L.) Cyrillo], fall panicum (Panicum dichatomiflorum Michx.), giant foxtail (Setaria faberis Herrn.), common ragweed (Ambrosia artemisiifolia L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.). In all species, most of those which lost viability did so within the first six months of burial.
Schafer and Chilcote (74) presented a model which described the changes in the physiological states among buried seeds. Seeds 6 introduced into the soil would be classified as dormant, nondormant, or viable. A reversability between nondormant and dormant seeds which appeared to be of ecological significance was indicated. The model allowed for a fraction of the seed bank to germinate under favorable conditions yet still allowed for long term persistence.
Viable seeds were lost in three ways: a) they germinated below their maximum depth of emergence, which resulted in death (in situ germination), b) lost viability due to aging, 01* c) lost viability by predation via soil organisms. They observed that perennial ryegrass seed (Lolium perenne L.) became nonviable after 60 days of burial in the field probably due to in situ germination.
Roberts and Feast (67) found that the average seedling emergence of sun spurge (Euphorbia helioscopia L.) was 71% for 2.5 and 7.5 cm depths, but only 30% for 15 cm depth. They indicated that seed populations in soil decline at an exponential rate. Their data from twenty species buried to a depth of 15 cm in the soil indicated that the population declined at a mean rate of about 12% per year, over a six year period. The rate of decline for individual species ranged from 6-21% per year.
Lewis (47) reported on the survival of several weed species after burial for 1, 4, and 20 years at three depths, in Aberystwyth,
Wales. If seeds survived for four years they usually remained viable for the following 16 years. He found that the following weed species had the greatest seed survival: creeping buttercup
(Ranunculus repens L.) 53%, common lambsquarter (Chenopodium album
L.) 23%, and curly dock (Rumex cripus L.) 18%. 7
Stoller and Wax (81) buried several weed species at depths from
1.3 to 15 cm below the soil surface in Urbana, Illinois. In situ
germination increased with increasing depth and was greater than
seedling emergence for most of the weed species tested.
Stoller and Wax (82) observed that viability of several weed
species buried at depths from 2.5 to 15 cm in the soil decreased with time, with viability decreasing most rapidly at the 2.5 cm
depth.
Solano et al. (77) showed that maximum emergence of spurred anoda [Anoda cristata (L.) Schlecht] occurred when seeds were buried
1.2 cm, with only 40% emergence from 7.5 cm, and virtually no emergence from 10 cm or more.
Dawson and Bruns (26) buried seeds of barnyardgrass, green foxtail, and yellow foxtail [Setaria lutescens (Weigel) Hubb.] at
2.5, 10, and 20 cm. The majority of seedlings emerged from 2.5 cm.
Overall, the longevity of the seeds declined with time, and after 15 years of burial, no seeds were viable at any depth. Subtle differences in environmental conditions profoundly affected the longevity of seeds in soils.
Fall panicum [Panicum dichotomiflorum Michx. var. geniculatum
(Wood.) Fern.] seeds when buried at five depths for five years in two different soil types in Ontario, Canada (1) lost slightly more than 10% of its viability after storage in the soil over one winter, irrespective of depth. The emergence of seedlings from the silt loam soil decreased from the 1, 2, and 5 cm depths the first year, and was erratic in the second growing season. No emergence of seedlings occurred from the lower depths of 10 or 20 cm throughout 8
the duration of experiment. At the 54 month sampling time, the
germination of exhumed seed from the 20 cm depth in both soil types
had decreased to approximately 6.5%.
Brecke and Duke (12) observed that fall panicum seeds when
buried at 0, 1.3, 2.5, 5.1, and 7.6 cm at Ithaca, New York, resulted
in seedling emergence from 2.5 cm or less, with no emergence from
7.6 cm. Maximum emergence (39%) occurred from the 1.3 cm depth.
The majority of research with buried seeds has been conducted
in the northern United States, England, or Canada. Little research
of this type has been conducted in the southern United States. The weed species tested and the climatic conditions observed in those
experiments may not be applicable to the humid conditions observed
in the southern United States.
As pointed out by Dawson and Bruns (26), the subtle differences
in environmental conditions of the research area profoundly affected the longevity of seeds in soils. The effects of high soil temperatures also favor germination and reduce seed survival (74).
The higher soil temperatures for longer periods of time in the southern United States would make it extremely difficult to correlate the work done in England, Canada, and the northern United
States to that of weed seed longevity in the southern U.S., especially Louisiana.
In response to the lack of information on the longevity of weed species in the southern U.S., Egley and Chandler (28) initiated a buried seed study to last for 50 years. Their data for 2.5 years after burial, indicated that with only few exceptions, soil depth did not influence seed survival. A notable exception was the 9
relatively high viability for redvine (Brunnichia cirrhosa Gaertn.)
buried 38 cm at the six month sampling date compared to the low
viability of seed recovered from 8 and 23 cm. The percentage of
seeds still viable after burial for 30 months were spurred anoda
71%; purple moonflower (Ipomoea turbinata Lagescary Segura) 71%;
johnsongrass [Sorghum halepensa (L.) Pers.] 62%; velvetleaf
(Abutilon theophrasti Medic.) 58%; goosegrass [Eleusine indica (L.)
Gaertn.] 33%; hemp sesbania [Sesbania exaltata (Raf.) Cory] 24%;
common cocklebur (Xanthium pensylvanicum Wallr.) 18%; common
eveningprimrose (Oenothera biennis L.) 14%; large crabgrass
[Digitaria sanguinalis (L.) Scop.] 12%; sicklepod (Cassia
obtusifolia L.) 10%; common purslane (Portulaca oleracea L.) 10%;
white morningglory (Ipomoea lacunosa L.) 8%; redroot pigweed 7%;
prostrate spurge (Euphorbia supine Raf.) 6%; prickly sida (Sida
spinosa L.) 5%; redvine 3%; Florida beggerweed [Desmodium tortuosum
(Sw.) DC.] 3%; barnyardgrass 1%; and chickweed [Stellaria media (L.)
Cyrillo] 0%.
Gomes et al. (32) observed that maximum seedling emergence of
ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. var. hederacea],
white morningglory and entireleaf morningglory (Ipomoea hederacea
var. integriuscula Gray) occurred from depths of 1.3 and 2.5 cm
below the soil surface.
Bannon et al. (5) reported that wild poinsettia seedlots
collected in different years showed significant differences in
germination, possibly due to differences in the environment under which the embryo developed. Maximum germination of wild poinsettia was observed at 25/35 C. Overall germination was influenced by both 10
temperature and light. An increase in gemination resulted from an
increase in temperature up to 35 C in laboratory and field
experiments. The heaviest periods of gemination in the field occurred in late spring and early summer when soil temperatures
reached the levels of the laboratory experiments (5, 62).
Bannon et al. (5) observed field germination of approximately
45% of wild poinsettia seeds under field conditions when buried 5 and 15 cm.; whereas, approximately 5% germinated from 30 cm. From a different seed lot buried the following year, approximately 90, 21, and 0% germinated at the 5, 15 and 30 cm depth, respectively.
Domant seeds constitute the major source of weeds in cropland, and a persistant seed bank is characteristic of many of the more serious agricultural weeds (10, 26, 43, 47, 66, 67, 74, 87).
The longevity of weed seeds in the soil depend upon several factors such as the environmental conditions surrounding the seed, the type or degree of domancy, and the depth of seed burial.
Harper (35) stated that the survival of viable seeds depends on the nature and degree of innate domancy, whether or not induced dormancy can develop, and the ability of the seeds to persist when d o m a n c y is enforced.
Several summary statements can be drawn:
1. Generally, seed longevity increased with depth of burial;
2. Generally, maximum seedling emergence of most species
occurred from seeds between 0 and 7.5 cm deep;
3. Different seedlots of even the same species showed
differences in loss of seed viability, possibly due to the
relative differences in initial dormancy; 11
4. The majority of seeds which lost viability did so within
the first two years of burial;
5. Weed seed populations in the soil are depleted
predominately by in situ germination (65, 67, 81);
6. The specific environmental conditions of the burial site
affected the longevity of the seeds buried.
Studies discussed previously demonstrate the potential for
seeds of many weeds to remain viable in the soil for long periods of
time. They did not simulate conditions encountered with various
tillage practices used in agricultural production.
Chepil (21) recognized that buried seed studies needed to
include cultivation regimes in order to facilitate correlation of the results with actual agronomic field conditions. He initiated several short-term studies with five weed species subjected to various tillage operations. He concluded that periodic cultivations decreased the number of viable seeds remaining at the end of the fallow period when compared to areas that were undisturbed. This decrease was not attributed to any direct stimulating effect on germination by cultivation, but instead to the action of cultivation in bringing buried seed nearer the surface. He reported that the number of viable seeds of frenchweed remaining after one year in soil cultivated to 15 cm was three times that in soil cultivated to only 6 cm.
Roberts and Feast (67, 68) studied the longevity including tillage effects on various weeds when known quantities of seeds were placed in soil in open-ended earthenware cyclinders sunk into the ground. Periodic mixing of the soil within the cylinders was termed 12
tillage. The longevity of seeds near the surface was less than at
greater depths and longevity was greater in undisturbed soil than in
tilled soil. The decrease in the seed population (averaged over a number of species) was 12%/yr in the undisturbed soil and 32%/yr in
tilled soil. Roberts and Feast (68) indicated an exponential
decline in the number of viable weed seeds in the soil.
Although these studies provided useful information on the
longevity of weed seeds in disturbed versus undisturbed conditions,
they utilized some form of containers within the field. Few studies have been conducted with natural populations of weed seeds in field plots, with the use of standard cultural practices.
Brenchley and Warrington (13) greatly reduced the weed seed population in the soil by fallowing field plots for four years, although some weeds occassionally produced seeds during the course of this study due to ineffective fallowing operations.
The effects of three vegetable crop rotations on the weed seed population was studied by Roberts (63) for six years, with
"extensive seeding" occurring in the fifth year. Before this extensive seeding, he observed a 50%/yr decline in the weed seed population in the soil.
Roberts and Dawkins (66) conducted a six year study on a natural population of weed seeds with tilled versus undisturbed cultivation regimes. The replenishment of the weed seed population was prevented by applications of a contact herbicide. The population (averaged across all species) declined exponentially at a rate of 22%/yr in undisturbed soil, 30%/yr in soil "dug" twice a year, and 36%/yr in soil "dug" four times a year. The term "dug" 13
referred to a tillage operation of some kind, but the exact method
was not indicated.
The relationship between the number of seedlings emerging and
the number of seeds in the upper soil layer is complex, and
literature concerning this relationship presents varied results.
Roberts and Dawkins (6 6 ) reported that under a consistent
cultivation regime, the relationship between the total number of
seedlings emerging throughout the year and the number of viable
seeds present at the start of it was remarkably constant. However, when the seedling populations responding to single cultivations are
considered the variation was much greater.
Several studies show little correlation between the overall weed populations and the seed numbers in the soil (41, 46). Roberts and Hewson (69) stated that twice as many seedlings may emerge from a fine, firm seedbed than from a rough soil surface. Another major factor discussed was inadequate soil moisture. Roberts and Ricketts
(70) observed that when soil moisture was adequate the total seedling numbers represented 3 to 6 % of the seeds; when dry weather followed cultivation the percentage was lower. The timing of soil cultivation from early March to mid-November had little effect on the percent of seeds which gave rise to seedlings, provided there was adequate soil moisture. In a rotation of vegetable crops with frequent soil disturbances, about 1 0 % of the viable seeds in the top
15 cm of soil gave rise to seedlings during the year (64). Values of 7% and 9% of the viable seeds in the top 23 cm was obtained on uncropped plots cultivated twice or four times a year, respectively
(66). 14
Standifer (78) conducted a two year study of weed seeds in vegetable cropping systems in Louisiana to which no seeds were added during the course of the study. In continuously cropped plots rice flatsedge (Cyperus iria L.) seeds at 0 to 5 cm depth declined to 24% of the original population, with no significant change in the 15 to
20 cm depth. Goosegrass declined to almost 0 in the 0 to 5 cm layer and to 19% in the 15 to 20 cm zone.
Lueshen and Anderson (49) initiated a field study in Minnesota aimed at determining the time required for eradication of velvetleaf seeds from soil under various land uses. Seven cropping or fallow programs were tested for their effects on the longevity of the velvetleaf seeds in the soil. The range of the remaining seed populations was from 10 % of the original under intensive tillage up to 56% under continuous alfalfa. The authors pointed out that the
10% figure still represented 1300 viable seeds per m 2 of field area.
Competition from weeds. Plant competition has been defined (3, 11,
27, 36, 50), but the exact meaning is confused by usage in the literature. Harper (36) in an attempt to clarify the numerous definitions adopted the term 'interference.' He defined interference as "comprising all changes in the environment, brought about by the proximity of individuals, including neighbour effects due to the consumption of resources in limited supply, the production of toxins, or changes in conditions such as protection from wind, and influences on the behavior of predators."
Clements et al. (23) outlined two major points of plant competition. The principles were, first: "Competition is keenest 15 when individuals are most similar and make the same demands on the
habitat and adjust themselves less readily to their mutual
interactions." Second: "The closeness of competition between plants of different species varies directly with their likeness in vegetation or habitat form."
These two principles proceeded the following definition of plant competition by Clements et al. (23): "Competition is a purely physical process with few exceptions, such as the crowding of
tuberous plants when grown too closely, an actual struggle between competiting plants never occurs. Competition arises from the reaction of one plant upon the physical factors about it and the effect of the modified factors upon its competitors. In the exact sense, two plants, no matter how close, do not compete with each other so long as water content, nutrient material, light, and heat are in excess of the needs of both. When the immediate supply of a single necessary factor falls below the combined demands of the plants, competition begins."
In general, plant competition refers to the competition for water, nutrients, and light. These three factors interact extensively; thus, change in one affects the plant response to the others.
Several studies have indicated that weeds caused greater yield losses in soybeans under moisture stress (61, 79, 80). Staniforth
(79) found a 15% yield reduction in soybeans due to yellow foxtail when soil moisture was severely limiting from mid-season until soybean maturity; however, only a five percent yield reduction occurred with adequate soil moisture. 16
The importance of early rainfall on weed establishment has been demonstrated (52, 79). Moolani et al. (52) found that the establishment of smooth pigweed was poor after soybean planting when
May rainfall was light, and soybean yield reductions attributed to this weed were less than during years of normal rainfall. Decreased soybean yields attributable to smooth pigweed and giant foxtail have been shown with periods of below normal moisture in June and July
(45, 52).
Research has established that competition for moisture usually occurs with other forms of competition (9, 55). Bauer et al. (9) observed that the response of barley or spring wheat to nitrogen fertilizer increased as precipitation or stored water increased.
Nelson and Nylund (55) found that depending on weed height, competition between weeds and peas primarily centered on light and water.
The competition for moisture by plants is a very complicated process. Plants vary greatly in their ability to extract and utilize soil moisture. In order to minimize the effects of moisture stress, crops should be kept weed-free.
Competition for nutrients constitutes an important aspect of weed-crop competition. Loomis (48) suggested that weeds provided keener competition for nutrients than for water.
Several studies have indicated that weeds compete for essential nutrients and decrease crop yields even at high rates of fertilization (54, 83, 8 8 ). Alkamper (2) in reviewing papers on nutrient competition emphasized that weeds derive greater benefits than crops because they usually absorb fertilizer more efficiently. 17
The interaction of competition for nitrogen with other factors
has also been investigated (38, 96). Addition of nitrogen and
removal of three cornered jack (Emex australis Steinh.) bolstered
wheat yields (38). An increase in the number of grain-bearing
tillers per plant was attributed to the effect of nitrogen. Witts
(96) studied the interaction of nitrogen competition with
temperatures and growth of wheat in England. He obtained a lower
response from wheat top dressed with nitrogen in May as oppossed to
March. The response was accentuated in both instances when weeds
were present.
The amount and disposition of leaf surface as a decisive plant
competition factor was realized as early as 1907 by Clements (22).
The competition for light in plants may operate throughout their
life cycle except when plants are young. "Competition for light is
not immediately competition between species, nor even between
plants. It is competition between leaves," Donald observed (27).
Rapid and higher growth, larger leaves, and climbing devices enable weeds to compete with crops for light (29).
There have been numerous methods for studying weed-crop
competition. Segar (72) outlined five basic methods: 1. Friesen's method; 2. survey; 3. screening; 4. logarithmic; 5. model
systems. Friesen's method involved permitting natural or specific
densities of weeds to grow or maintaining a crop weed-free for predetermined periods of time and then determining yield reductions.
The survey method involved comparing weedy and weed-free plots over a large range of environments to determine yield reduction.
Screening methods, usually performed in the greenhouse, have been 18
used to define the characteristics which endow weeds with a
competitive advantage. The logarithmic technique involves the
sowing of weeds in logarithically increasing population densities
along a strip of crop to assess weed impact on the crop. The model
system primarily involves growing crops and weeds separately and in
various combinations in an attempt to develop a mathematical
predictive equation.
The Friesen's method allows one to determine the "critical
period for weed control" defined by Nieto et al. (57) as the time
span when weeds present from the beginning of the crop cycle must be
removed or the point after which weed growth no longer affects crop
yield. Burnside and Wicks (17) observed that a weed-free period
(WFP) of four weeks after planting was needed for maximum yields of
sorghum [Sorghum bicolor (L.) Moench] in Nebraska when the field had
mixed annual weeds present.
Hill and Santelmann (39) reported that a WFP of six weeks was
needed for maximum peanut (Archis hypogaea L.) yields. The weed
population consisted of smooth pigweed (Amaranthus hybridus L.) and
large crabgrass. Buchanan et al. (16) reported that for maximum
production of peanut foliage in fields with sicklepod infestations,
a WFP of four weeks was usually sufficient. For maximum yield in
cotton (Gossypium hirsutum L.), a WFP of approximately eight weeks was necessary for fields infested with mixed annual weeds (14) and
five to six weeks for fields infested with prickly sida (Sida
spinosa L.) (15).
Few researchers have investigated the weed-free period required
immediately after soybean emergence to obtain maximum yields with 19
natural infestations of weeds. The WFP required for maximum yield
of soybeans depends upon the weed species present. Thurlow and
Buchanan (8 6 ) reported that in fields with sicklepod infestations, a
WFP of two weeks was required for maximum yields. Early- and
late-planted soybeans required a three week WFP with cultivations to
achieve maximum yields (53). Barrentine (8 ) observed that soybeans
required a four week WFP for maximum yields when the major weed present was cocklebur. A WFP of six to eight weeks was needed for maximum yield of soybeans when the major weeds present were common and ivy-leaved morningglory (95).
The literature available for the influence of soybean planting date on weed competition is limited. Planting, initiation of
flowering, and maturity dates of various soybean cultivars are determined by their response to photoperiod (37). Vegetative growth of cultivars adapted to the southern United States is almost complete when flowering begins because of their determinate growth habit. Therefore, less vegetative growth is made with late rather than early plantings which could reduce crop competitive ability.
Planting date studies conducted in Louisiana in 1957-58 indicated that soybean yields and vegetative development were greater when planted in May than late June (33). The maximum yield of soybeans was reported for the early May planting date. Increased weed growth in the late-June plantings was reported, and attributed to less soybean canopy development. In Virginia, late-June and early-July plantings were not as effective in shading between rows as plantings on May 6 or May 20 (76). 20
Several studies have shown a decrease of 10 to 50% in seed yield, plant height, number of nodes, and branching in both determinate and indeterminate genotypes of soybeans planted after mid-June (18, 60, 75, 93). Maturity, flowering, and canopy closing dates were delayed in late plantings.
Oliver (58) noted that artificially infested velvetleaf did not appear to have the potential to become a major weed problem in
Arkansas for soybeans planted in June due to its photoperiodic response and, subsequently, decreased season competitiveness. He stated that "the weed could present problems for soybeans planted early, especially when an early maturing variety is used" (58).
Murphy and Gossett (53) conducted field studies to determine the influence of two soybean planting dates on (a) the length of early-season weed control required to achieve maximum soybean yields; and (b) the rate of shade development and suppression of weeds by soybeans at Florence, South Carolina. Planting dates were
May 11 and June 28, 1978, and May 14 and July 2, 1980. The periods of weed-free maintenance (0, 3, 5, 7, 9, 11 weeks, and all season) were achieved by hand-weeding and hoeing. Cultivation was performed on all plots in order to confine the weeds to a 15-cm band within the soybean row area. At soybean maturity, soybean seed yields, and fresh weed weights were determined. Weed species present in this study were redroot pigweed, large crabgrass, goosegrass, crowfootgrass [Dactyloctenlum aegyptium (L.) Richter], tall morningglory [Ipomoea purpurea (L.) Roth], and spiny amaranth
(Amaranthus spinosus L.). To prevent reinfestation by the weeds present in this study, 5 weeks of WFP was required for the 21
early-planting date and only 3 weeks of WFP needed for the
late-planting date. Their data showed that for maximum soybean
yields, a 3 week WFP was needed regardless of planting date.
Harger and Nester (34) stated that maximum wild poinsettia
germination occurred in June when soil temperatures were high.
Better wild poinsettia control resulted with soybeans planted in
early May. This allowed soybeans to become established before the wild poinsettia emerged. It was hypothesized that shade from the
soybean canopy may have reduced soil temperature fluctuations
sufficiently to reduce wild poinsettia germination.
Determinate cultivars have shown a yield response to narrow row
planting, although these responses usually occurred in late plantings (after June 15) rather than in early plantings (19, 75,
91, 92, 93). The narrow row width (less than 0.50 m) should be used
for soybeans planted (after June 15) because of the increase in yield and an increase in weed control due to early canopy closure.
Effect of cultivation. Klingman (44) noted that the first to suggest the planting of crops on rows, so as to permit
"horse-hoeing" of weeds between the rows, was Jethro Tull, in 1731 in Horse Hoeing Husbandry. Pavlychenko (59) viewed cultivation as a necessary means of weed control. He emphasized the use of "shallow cultivation," (not deeper than 2.5 cm to prevent injure crop roots) to remove all top growth of the weeds (59). He considered that if the top growth was continually suppressed, the root would die by starvation. 22
The general consensus from older literature is that the main
value of cultivation is to control weeds. In most cases, other
benefits from cultivations such as increased nitrification,
increased penetration of rainfall, formation of soil mulch to reduce
evaporation, aeration, and loosening the soil have been shown to
contribute practically nothing to increasing yields on many soils.
However, in certain situations, cultivation has been shown to be of
some advantage other than weed control (40, 71).
Peters et al. (62) indicated that when herbicides were used,
soybeans in 81 and 102 cm rows usually needed at least one and
sometimes two cultivations for good weed control and high soybean yields. Gebhardt (30, 31) reported that a cultivation, in addition
to the herbicide treatments used, was necessary for improved weed
control and increased soybean yields. McWhorter and Barrentine (51) noted that the use of cultivation in combination with herbicides for
control of cocklebur produced significantly greater soybean yields
than did the use of herbicides alone.
Although the use of herbicides has decreased the number of
cultivations necessary, most farmers still depend upon at least one
cultivation to supplement the weed control obtained with herbicides except where minimum tillage methods are employed.
Chacteristics and control of wild poinsettia. Wild poinsettia, originally a native plant of tropical and sub-tropical America, is now widespread in the tropics as a weed of cultivated land and waste places (42) . It has been reported as a serious weed problem in soybeans in the lower Mississippi River alluvial flood plain (4, 6 , 23
34, 56, 89) and in southern Alabama (4). Sanders (73) reported wild poinsettia as one of the ten most troublesome weeds in Louisiana
soybeans.
Wild poinsettia was described as an erect, usually unbranched, annual herb between 30 and 80 cm high which contains a white latex
(42). Alternate leaves which are variable in shape and size are whorled towards the top of the stem. A flat dichotomously branched
terminal inflorescence of small yellow flowers is subtended by large
leafy bracts often with a bright red or cream patch at the base.
The inflorescence consists of clusters of numerous, small,
short-stalked, flowers lacking petals or sepals but with conspicuous glands surrounded by radiating leaf-like bracts.
The fruit is a hard-coated, three-lobed capsule with reddish blotches containing three seeds. Seeds are 2.0 to 2.5 mm in diameter, ovoid in shape, dark brown to black in color, and have a rough surface (4). Seeds are shed by forceful dehiscence of the capsule triggered by drying. Seeds are commonly dispersed up to 1 m from the plant (4).
Wild poinsettia is very competitive, especially in the early stages of establishment, due to its ability to grow very rapidly and form a dense canopy over young crop plants (4, 89, 94).
When wild poinsettia were planted in soybeans at a rate of eight plants per meter of row, yields were reduced by 18, 22, and 33 percent when poinsettia were allowed to compete for 8 weeks, 12 weeks, or full season, respectively (34, 56).
The latex contained in wild poinsettia plants can cause dirt and vegetation to adhere to the harvested beans reducing the final 24 quality, and increasing the moisture content (56). Dense populations of wild poinsettia in soybeans reduce yields through competition and by impairing harvest (56).
Harger and Nester (34) reported that metribuzin
[4-amino-6-(1,1-dimethylethy1)-3-(methylthio)-1,2,4-triazine-5(4H)- one] at 0.6 kg ai/ha normally provided 70 to 90 percent control of wild poinsettia and was the most effective soil-applied herbicide.
Although metribuzin provided good control, it was detoxified rapidly in the soil, and control normally deteriorated after two to three weeks, necessitating the use of postemergence herbicides (34).
Overtop herbicides that provided the most effective control were the sodium salt of bentazon [3-isopropyl-lH-2,l,3- benzothiadiazin-4(3H)-one 2,2-dioxide] and the sodium salt of acifluorfen [5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzic acid] when applied before the wild poinsettia was more than 10 cm tall (4, 6 , 34, 56). When soybeans were 13 to 15 cm tall, directed postemergence applications of dinoseb [2 -sec-buty1-4,6 - dinitrophenol] and dinoseb plus naptalam [2 -[(1-naphthalenylamino) carbonyl)benzoic acid]] have shown excellent control of wild poinsettia (4, 6 , 34, 89). When soybeans were 20 to 25 cm tall, a postemergence directed application of either metribuzin or the dichloride salt of paraquat (l,l'-dimethyl-4,4,-bipyridinum ion) provided excellent control of wild poinsettia plants less than 10 cm in height (34, 89).
For full season control of wild poinsettia, a weed control program consisting of preemergence and postemergence (over top and post directed) herbicides along with inter-row cultivations would be required. Davis et al. (25) suggested that the best control could be obtained with a combination of inter-row cultivations backed up by herbicides. Wilson (94) stated that "the main difficulty in the chemical control of wild poinsettia is its resistance to most of the herbicides used for broadleaved weed control." MANUSCRIPT
26 Behavior of Euphorbia heterophylla Seed Bank*
VERNON B. LANGSTON and THOMAS R. HARGER2
Abstract. Short term burial of freshly harvested seed and soil
disturbances in agricultural populations of wild poinsettia 3 (Euphorbia heterophylla L. # EPHHL) indicated a very low carry over
of seeds into the second season after dissemination. After seeds were buried at 10, 50, 100, and 200 mm in the fall; 4%, 81%, 30%,
and 1%, respectively, produced seedlings during the following
growing season, and only 3%, 1%, < 1%, and 3% of the seeds,
respectively, were viable after 1 yr. Soil disturbances (tillage)
did not affect seedling recruitment or longevity of wild poinsettia
seed. Early planting dates (May 1) of soybeans required 6 weeks of weed-free maintenance to prevent serious reinfestation and
subsequent yield reductions in fields with a high agronomic seed bank of wild poinsettia, whereas for late planting dates (June 10) 3 weeks of weed-free maintenance was required. No significant difference in yield was detected between one or two cultivations for either planting date.
Additional index words. Seed longevity, reinfestation, seedling emergence, weed ecology, soil disturbances, Euphorbia heterophylla
L. # 3 EPHHL.
27 28
Received for publication and in revised form
These data are from the Ph.D. dissertation of the first author. 2 Grad. Res. Asst, and Assoc. Prof., respectively, Dept. Plant Path.
and Crop Physiol., Louisiana Agric. Exp. Stn., Louisiana State Univ.
Agric. Center, Baton Rouge, LA 70803. 3 WSSA-approved computer code from Important Weeds of the World, 3rd
ed. , 1983. Available from WSSA, 309 West Clark St., Champaign, IL
61820.
INTRODUCTION
Wild poinsettia is a major weed in Louisiana soybeans [Glycine max (L.) Merr.]. Dormant seeds constitutes the major source of weeds in cropland, and a persistant seed bank is a chacteristic of many troublesome agricultural weeds (3, 11, 14, 21, 22, 25, 28).
A voluminous amount of data on response of seed to environmental
stimuli and copious extrapolations of these data to ecological behavior of plants including agricultural weeds. However relatively
few studies have attempted to document seed bank dynamics of agricultural weeds under field conditions. A better understanding of seed bank dynamics is essential for the development of logical management strategies of agronomic weeds.
The longevity of weed seed in soil depends upon several factors including environmental conditions, the type or degree of dormancy and its depth of burial. Harper (7) stated that the survival of seeds depends on the nature and degree of innate dormancy, whether induced or secondary dormancy can develop, and the ability of the 29
seeds to persist when dormancy is enforced. Seed longevity which would encourage a buildup of a large seed bank increases the persistence of weed populations and decreases the significance of
the contribution of seeds produced during one season to future weed problems. Seedling recruitment decreases the seed bank, and if no plants are allowed to produce seeds the seed bank will eventually be depleted. A knowledge of seed bank characteristics (temporal germination, seed longevity, and seedling recruitment) will enable weed scientists to develop more effective control programs.
Roberts and Dawkins (21) reported that a natural population of mixed weed species declined exponentially at a rate of 2 2 %/yr in undisturbed soil, 30%/yr in soil "dug" twice a year, and 36%/yr in soil "dug" four times a year. The term "dug" referred to an undefined tillage operation. Under any one cultivation regime, the relationship between the total number of seedlings emerging throughout the year and the number of viable seeds present at the beginning was remarkably constant; however, when the seedling recruitment in response to a single cultivation was considered, the variation was much greater.
Several studies have shown little correlation between weed densities in crops and the number of seed in the soil (1 0 , 1 2 ).
Roberts and Hewson (23) stated that on a fine, firm seedbed twice as many seedlings may emerge compared to a rough soil surface. Roberts and Ricketts (24) observed that when soil moisture was adequate, total seedlings represented three to six percent of the seeds. When dry weather followed cultivation, the percentage was lower. The timing of soil cultivation from early March to mid-November had 30
little effect on the percentage of seeds which gave rise to
seedlings, provided there was adequate soil moisture (24). In a
rotation of vegetable crops with frequent soil disturbances, about
10% of the viable seeds in the top 15 cm of soil gave rise to
seedlings during a year (19). Values of 7% and 9% of the viable
seeds in the top 23 cm was obtained on uncropped plots cultivated
twice or four times a year, respectively (2 1 ).
The temporal seedling emergence of wild poinsettia has not been
investigated. Data presented by Bannon et al. (1) indicated
longevity of wild poinsettia seeds under field conditions in
Louisiana may be considerably less than that reported for many weeds. Freshly harvested seedlots of wild poinsettia were buried
50, 150, and 300 mm in October in each of two years. In July
following the first burial, 55% remained viable at 50 and 150 mm while 95% were viable at the 300 mm. In July following the second burial, approximately 10, 79, and 100% were viable at the 50, 150, and 300 mm depths, respectively.
The magnitude of crop interferences is determined by two distinct phenomena. The quantity of seedlings recruited during the time the crop is present (planting till harvest) and the success (growth and reproduction) of seedlings during the crop depending on the time of recruitment relative to crop domination of the area. Many researchers investigated the interaction of weed and crop plants after emergence; however, few investigated the interaction of crop management with the seed bank. The weed-free period (WFP) required immediately after soybean emergence to obtain maximum yields in an 31 agronomic seed bank of mixed weeds depended upon the weed species present (2, 16, 27, 29).
In most date of planting studies yield was usually considered to be a response of vegetative growth to either day length or seasonal moisture trends (6 , 9). Very few attempt to relate planting date to the behavior of the weed seed bank.
Prior to herbicide development the general consensus was that the main value of cultivation was to control weeds. Several reports indicated that the use of cultivation in addition to herbicides resulted in higher yields (4, 5, 15, 18). This could have been due to either increasing weed control or improving soil conditions.
Other studies have indicated that cultivation can stimulate seedling emergence (2 1 , 2 2 ); therefore, its impact on late emerging weeds should be considered. Post-planting cultivation remains a standard practice in row crops in southern United States.
The objectives of this research were: a) to determine the viability and germination of wild poinsettia seeds buried at different depths over one and two year periods; b) to determine the influence of different frequencies of soil disturbances over a two year period on seedling emergence and longevity of a normal agronomic seed bank of wild poinsettia; c) to quantitate the reinfestation of soybeans from an agronomic seed bank of wild poinsettia as affected by planting dates and post-planting cultivations after seedlings were removed at 0, 3, 6 , and 9 wks after planting. MATERIALS AND METHODS
Three field studies ("buried seed", "seed depletion", and
"reinfestation") were conducted near Baton Rouge, Louisiana on a
Mhoon silty clay loam soil (fine silty, mixed, nonacid, thermic
Typic Fluavaquents) with a pH of 6.5 and organic matter content of
1.1% in the 0 to 150 mm layer.
Buried seed experiment. Wild poinsettia seeds were harvested by hand picking elevated, individual three seeded capsules from field grown plants between 7:00 and 9:00 a.m. Mature capsules are elevated above those less mature by elongation of the peduncle.
Capsules found to be elevated early in the morning normally forcefully dehisce as they dry during the day. The collected capsules were placed in a mesh bag and allowed to dehisce in the laboratory. Seeds were then cleaned in a forced air column and stored in sealed containers at 5 C until burial (approximately 15 and 10 days in 1981 and 1982, respectively).
In 1981, eight lots of 100 seeds each were buried in separate excavations at each of four depths. To facilitate recovery, seeds were buried in 0.3 by 0.3 m screen trays with 0.05 m sides. Seeds were mixed in sufficient soil to form a 10 mm layer in each tray then placed so that the bottom of the tray was at either 10, 50,
100, or 200 mm. Therefore, each indicated burial depth was actually from that depth to 10 mm less. The experiment was a completely randomized design conducted in an area free of wild poinsettia.
Seedling emergence from all burial sites was determined during the
1982 growing season. The burial sites were observed weekly, and seedlings were counted when "flushes" occurred. After counting, the
32 33
seedlings were destroyed, and the entire area was maintained free of
vegetation by spraying either the isopropylamine salt of glyphosate
[N-(phosphonomethyl)glycine] or the chloride salt of paraquat
(1,1'-dimethyl-4,4'-bipyridinium ion).
On October 15, 1982, four seed lots which had been randomly
selected at the time of burial were removed to determine the number
of seeds remaining viable. On the same day, fresh seed collected in
1982 were buried in the same excavations. Seedling emergence from
the 1981 and 1982 buried seeds were determined during the 1983
growing season. On September 15, 1983, all buried seeds were removed and the number remaining viable determined. When seeds were
recovered, the lower 20 mm of soil (except in the 10 mm depth where
all soil was removed) was removed to insure recovery of all seeds.
Analysis of covariance was performed and LSD at P. = 0.05 was used to locate significant differences among treatments. The
seedling emergence in 1982 was replicated eight times. The
remaining data was replicated four times.
Seed depletion study. A separate area of the field was managed during 1980 and 1981 to produce a uniform high density of wild poinsettia. After seed dispersal in 1981, the area was thoroughly disked to a depth of 0 . 1 2 m then smoothed with a field harrow.
In the spring of 1982, plots measuring 3 by 5 m were established in a randomized complete block design with four replicates per treatment. Plots were subjected to various tillage treatments as follows:
None: The soil was not disturbed. 34
1X-E: Tilled once each year in the early spring (5-10-82 and
4-25-83).
1X-M: Tilled once each year in the summer only (6-1-82 and
6-3-83).
2X-E,M: Tilled twice each year, once in the early spring and
once in the summer (same dates as 1X-E and 1X-M).
2X-M,L: Tilled twice each year in the summer (same dates as 1X-M
plus 6-24-82 and 7-5-83).
3X-E,M,L: Tilled three times each year (same dates as previous
treatments).
The tillage operation referred to the use of a power tiller
operating to a depth of 60 mm.
The beginning seed bank was determined by taking 3 soil cores
(150 mm diameter) within each plot from the 0-60 and 60-120 mm
depths. Seedling emergence was determined during the 1982 growing
season, then the plots were sampled again on October 18 and 19, in
the same manner except 6 soil cores per plot were taken to determine
the number of viable seeds remaining after one growing season.
Seedling emergence was again monitored during 1983; however, because of the reduced number of seeds found after one season and
decreased seedling emergence in 1983, soil samples were not taken after the 1983 growing season. Wild poinsettia seedling emergence was determined by counting the number present in 2 randomly placed
0.50 by 0.50 m quadrats in each plot. Seedling density was evaluated only when significant emergence occurred in at least one
treatment. After counting, all plants were destroyed by applications of glyphosate or paraquat. A 3 m border area was 35
maintained around the plots to prevent the dissemination of seeds
into the test area.
Analysis of variance was performed, and LSD at P. = 0.05 was used
to locate significant differences between treatments means.
Determination of seed viability. To separate the seeds, soil
samples from both studies were dispersed by placement in 2 liter
glass jars containing 1 to 1.5 liters of water and shaken for
approximately 12 hrs at 60 cycles per minute. The soil slurry
containing the seeds was then placed on a 1.7 by 1.7 mm seive and
washed with a fine spray of water until all soil was removed. The
remaining seeds were placed in water. Previous studies indicated
that seeds which would float were either empty seed coats or decayed
seeds. Those seeds which did not float and were firm to the touch were counted as recovered seeds and germination was determined.
Seed which did not germinate and were still firm after the
germination test were evaulated for viability using 2,3,5-triphenyl
tetrazolium chloride (TTC) (13).
Seed germination was attempted by placing the seeds in 90 mm petri dishes on 2 Watsman #3 filter papers which had been moistened with 10 ml of water. The petri dishes were placed in an incubator
set at 25/35 C on alternating 12 hr cycles with no light (1). No attempt was made to exclude light from the seed during soil removal or when checked periodically for germination. Germination was determined as the emergence of a radicle through the seed coat.
Individual germinated embryos and decaying seeds were recorded and removed approximately every 5 days. After 30 days, any seeds which were still firm were treated with 0.1% TTC (w/v) at pH 7.3 (13). 36
After an additional 24 hrs incubation in TTC, the seeds were cut
open and seeds with red embryos were recorded as viable.
Characterization of seedlots used in the buried seed study was conducted in the same manner at the time each lot was buried.
Reinfestation study. The study area to be used each year was managed the previous year to provide a high density of wild poinsettia. The test area received 280 and 0 kg/ha of 0-24-24 fertilizer in 1982 and 1983, respectively. Each year the experimental area was plowed in the spring and a seedbed was prepared using a spring tooth harrow. The seedbed was reworked with a spring tooth harrow for the late planting date (LPD) each year to prepare a final seedbed. For the early planting date (EPD), Forrest soybeans were planted April 29, 1982, and April 28, 1983, and for the LPD, June 14, 1982, and June 7, 1983. The planting dates in both years was timed to coincide with periods of sufficient moisture for germination and stand establishment. Individual plots were four
0.8 m rows 5 m long.
The experiment each year was conducted in a split-split design with four replications. Main plots were planting dates arranged as a randomized complete block. Sub-plots were cultivation regimes randomized within planting dates and sub-sub plots were WFP randomized within cultivation regimes.
Cultivation was performed with a Lilliston R rolling cultivator either once (at 3 wk after planting, IX) or twice (at 3 and 6 wk after planting, 2X). During the 1983 season, due to wet conditions, the weed removal for 3 wks WFP (including the cultivation) for both planting dates was actually performed at 4 wks after planting. 37
Weed-free periods were obtained by removing weeds after 0, 3, 6 ,
and 9 wks from planting for each date of planting. The reference
treatment for yield was maintained weed-free throughout the season.
Wild poinsettia was removed after the 3 and 6 wks WFP using either
the sodium salt of bentazon [3-isopropyl-lH-2,1,3-benzothiadiazin-
4(3H)-one 2,2-dioxide] at 0.9 kg ae/ha or the sodium salt of
acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic
acid) at 0.6 kg ai/ha, as an overtop spray. After the 9 wks WFP the
alkanolamine salt of dinoseb (2-sec-butyl-4,6 -dinitrophenol) at 1.8
kg ae/ha was applied post-directed for weed removal. Plots were
rogued by hand after herbicide applications to remove any wild
poinsettia plants recovering. Plots were then allowed to reinfest
until harvest.
The effects of the treatments were evaluated by determining wild
poinsettia density and standing biomass at soybean maturity and yield of soybeans. Low weed densities were determined in the middles by counting the total number of plants remaining in the 0.50 m area actually tilled by cultivation between rows, and high densities were determined by counting plants in four 0.25 by 0.50 m quadrats randomly placed in the two middles. Data from middles were
taken from those without tractor wheel traffic. High densities were those greater than approximately 20 plants/m2. The density of wild poinsettia in the soybean row (150 mm on each side of the drill) was determined by counting the total number of wild poinsettia plants in the two center rows or by counting the number of plants in three random 1 m sections of row for low and high density plots, respectively. Average plant dry weight was determined from 10 representative plants taken from both the middle and the row areas
of each plot and dried to constant weight at 40 C. Standing biomass
(g/m2) for both the middle and row was determined by multiplying the
number of plants/m2 by the average dry weight (g/plant). The yield
of soybeans were determined by harvesting the center two rows of
each plot. Wild poinsettia plants remaining in the plots were hand
removed to facilitate harvest.
Yield data were subjected to analysis of variance. Because data
for density and standing biomass did not meet the assumptions for
analysis of variance, homogenity of variance and normality, the
Mann-Whitney U-Test for nonparametric comparisons was used (26).
Because there were no apparent differences in trends between the two years of the study, density and biomass data are presented as the
combined data for both years. Yield data are presented for each year.
Rainfall and temperature during the study were obtained from a
USDA weather station located approximately 500 m from the research site.
RESULTS AND DISCUSSION
Buried seed study. Initial characterizations of the 1981 seedlot was 96% germinated and 99% viable. The 1982 seedlot characterizations were 87% germinated and 99% viable. No seedling emergence was observed immediately after burial of either seedlot.
The temporal seedling emergence during the first growing season following burial is presented in Tables 1 and 2, respectively, for seed buried in the fall of 1981 and 1982. Significantly greater 39
total emergence occurred from the 50 mm depth during both years.
Emergence from the 50 mm depth accounted for 81% and 6 6 % of total
seeds buried at this depth in 1981 and 1982, respectively, and also
accounted for 70% and 71% of total seedlings emerging in the two
years respectively. The 100 mm depth (Table 1) accounted for the
next greatest emergence in 1982, comprising 30% of seeds buried at
that depth and 26% of total seedling emergence in that year.
Seedling emergence from the 10 and 100 mm depth was not different in
1983 (Table 2). Emergence from each of these depths accounted for
approximately 14% of the seeds buried at each depth, and the
combined emergence from both depths account for 28% of total
seedling emergence in 1983. Total seedling emergence from all
depths in both years was similar, accounting for 28% and 23%,
respectively in 1981 and 1982 of the seeds buried at all depths.
The temporal emergence pattern during the two years was
different, being generally earlier in 1982. In 1982, 45% of total
seedling emergence occurred prior to April 2 (Table 1). Emergence
from the 50 mm depth accounted for 99% of this flush. A second major flush occurring between May 10 and May 20 accounted for 39% of total seedling emergence for this year. Seeds buried at the 50 and
100 mm depths contributed equally to this second flush, emergence from each depth accounting for greater than 49% of this flush.
These two flushes accounted for 84% of the total emergence in 1982.
In 1983, emergence occurred in 3 major flushes which accounted for 85% of total seasonal emergence (Table 2). The largest flush, counted on May 27, accounted for 38% of total emergence for the year and flushes counted on June 10 and July 5 accounted for 40 approximately 24% each of the total emergence. The average relative contributions to total seedling emergence for each of these flushes was 20%, 6 8 %, and 11% for the 10, 50, and 100 mm depths, respectively, and was similar for each date. Total emergence from the 2 0 0 mm depth accounted for 1% or less of total emergence in each year. No seedlings emerged during 1983 from seeds buried in October of 1981.
Because viability of the buried seeds was not known at any time between burial and the end of the growing season, it was impossible to relate seedling emergence to number of viable seed at any time during the emergence period. Seeds buried at the 10 mm depth may have become nonviable during the winter or dryer conditions near the soil surface may have caused greater embryo mortality during the spring and summer. Although not monitored during this study, predation and attack by disease organisms are additional factors which could contribute to loss of seed viability. The few seedlings which were established from seeds buried at 2 0 0 mm were often observed to have emerged through soil cracks which occurred during dry periods. It was reasonable to assume that seedling emergence would have been severely impeded for seeds buried at 2 0 0 mm.
No obvious relationship was observed between the major germination flushes and the rainfall pattern during the growing season (Figure 1). The difficulty in attempting to relate weather patterns to emergence flushes is knowing when germination was initiated. Seedlings counted on any given day could have emerged anytime during the previous week. Also, emergence could occur at various times after germination, depending on the depth of burial, 41
soil cracking, and environmental conditions following germination which could influence seedling vigor or physical resistance of the
soil to an emerging seedling. The trend toward later emergence in
1983 compared to 1982 was not a result of soil moisture in that the
spring of 1983 received greater precipitation than 1982. The early
spring of 1983 was also cooler than the spring of 1982, which could have reduced or delayed seedling emergence (Table 3). The temporal
emergence pattern of seedlings can be considered to be a result of
two environmental influences, one being the condition which causes
the seed to lose dormancy, and the other being a condition which
either triggers germination or allows it to be successful. A more
thorough chacterization of the microenvironment surrounding buried
seed and a better understanding of factors which control dormancy
and germination of wild poinsettia under field conditions are needed
to understand the relationship between environmental conditions and
seedling emergence.
The number of viable seeds recovered from the buried seed study
is shown in Table 4. Very few seeds remained viable after one year of burial at any depth. There was a tendency for more seed to remain viable after one year at the 200 mm depth for the 1982 seedlot. Because of the low numbers, statistical tests may be questionable; however the trend was compatable with the initial characterizations of the two seedlots which indicated a greater degree of germination and, therefore, possibly less dormancy in the
1981 seedlot.
The majority of seeds buried in this study became nonviable without producing seedlings [100%-(total seedling emergence (Tables 42
1 and 2) + viable seeds recovered (Table 4))]. The average number
of seed for both burial dates which became nonviable was 8 8 %, 24%,
77%, and 97% for the 10, 50, 100, and 200 mm depths, respectively.
Seed depletion study. Seedling emergence in the seed depletion
study showed that soil disturbances did not stimulate the emergence
of wild poinsettia seedlings (Table 5). There were no differences
in seedling emergence of wild poinsettia at any of the observation
dates for either year. Seedling emergence prior to June 23, 1982,
accounted for 98% of the total seedlings emerging during the two
years. This compares to 99% of total seedlings emerging prior to
June 23 from the seeds buried in October of 1981.
The results of seed bank samples of the 0 to 60 and 60 to 120 mm
depths in the seed depletion study are presented in Tables 6 and 7,
respectively. As would be expected, there was no difference in the
base sample from either depth taken prior to any cultivation. There were also no differences indicated between any of the cultivation
treatments from samples taken in October of 1982. No viable seeds were detected in the 60 to 120 mm depth after only one season.
Because of the low number of seeds detected in the 0 to 60 mm
samples, it was felt that the sampling technique was inadequate to
show any differences which may have resulted from cultivation treatments; therefore soil sampling was not done in the fall of
1983. It can be concluded that because of the rapid decline in the seed bank ( >99% in the 0 to 60 mm depth) in all cultivation regimes cultivation was not a major factor in determining the number of viable seeds remaining in the seed bank of wild poinsettia. 43
Total seedling emergence in the seed depletion study accounted
for 59% of the viable seeds detected in the base sample. This
result was not directly comparable to the buried seed study because
the number of buried seed remaining viable the following spring was not known.
Reinfestation study. The density of wild poinsettia plants in
the row for the reinfestation study is shown in Figure 2. The different cultivation regimes had no significant effect on density
in the row except after the 3 wk WFP for the LPD where there was a marginal significance of the 2X cultivation being less than the IX cultivation. When no wild poinsettia plants were removed (0 wk WFP) there were approximately four times more plants in the LPD than EPD.
After removal at three or six wks, the trend was reversed in that there were fewer plants in the LPD than the EPD. The smaller density in the EPD was possibly the result of cooler temperatures or a greater dormancy in the seed bank leading to fewer seedlings emerging after planting. Seedlings which did emerge, in addition to the developing soybeans, were able to suppress the establishment of subsequent seedlings. At the LPD for the 0 wk WFP a greater number of seedlings emerged shortly after planting but before the area was dominated by soybeans, and these were able to survive until harvest.
This trend was reversed after the 3 and 6 wk removal, possibly because few seedlings of wild poinsettia emerged after these dates as suggested by data from the buried seed study. In 1982, 12% of total seedling emergence from buried seed occurred after the date of
3 wk removal for EPD, whereas approximately 1% occurred after the date of 3 wk removal for LPD. In 1983, nearly 100% of total 44
seedling emergence from buried seed occurred after the date of 3 wk
removal for EPD, whereas approximately 10% occurred after the date
of 3 wk removal for LPD. Therefore, there may have been less
emergence pressure after the same WFP following the two planting 4 dates. Data from Shrefler , plus the small number of seeds
remaining viable after one season of burial suggested that lack of
emergence was due to exhaustion of the seed bank. Another possible
explanation would be more vigorous soybean growth from the second planting date which could have competed more effectively with
emerging wild poinsettia. Another effect indicated in Figure 2 was
the lower density of wild poinsettia at the 3 wk WFP or greater from either planting date when compared to the 0 wk WFP. This is probably a combination of reduced seedling emergence and greater competition from established soybeans.
Plant density in the middles is presented in Figure 3. A trend difference between the data for density in the middles when compared to density in the row was the significant difference between one and two cultivations for the 0 and 3 wk WFP. This would be expected because these data were taken from cultivated areas within the plot.
Cultivation resulted in essentially complete removal of weeds from the tilled area. Since cultivations occurred at 3 and 6 wk after planting the differences would indicate greater emergence after 3 wk
4 Shrefler, J.W. 1983. Studies on the behavior of seeds and seedlings of wild poinsettia (Euphorbia heterophylla L.) as a soybean weed. Unpublished M.S. thesis, Dept. Plant Path, and Crop.
Physiol., Louisiana State Univ., Baton Rouge, LA 70803. 63pp. 45
for IX cultivation then after 6 wk for 2X cultivation. There were
no significant differences between the 0 and 3 wk WFP as groups for
the EPD. This was again expected because the density was the result
of emergence after cultivation on the same date for both WFP. There
was no obvious explanation for the difference between the 0 and the
3 or 6 wk WFP at the LPD. The difference in density between the 0
and 3 wk WFP at EPD compared to the 6 wk WFP at the EPD indicated
less seedling emergence after the 6 wk WFP.
The 3 wk WFP, IX cultivation treatment for the EPD had
approximately 6 times greater density in the middle than in the row
(Figures 2 and 3). This should not be interpreted as stimulation of
emergence by cultivation. The cultivation for this treatment
occurred prior to the planting of the LPD, therefore the potential
for emergence in this treatment would have been as great or greater
than emergence in the LPD, 0 wk WFP (Figure 2) which was
considerably more. The lower density in the middle for the EPD, 3 wk WFP, IX cultivation compared to the row of 0 wk WFP for the LPD may be the result of suppression of seedlings by the soybean canopy
even in the middle. The difference between the row and the middle
for the EPD, 3 wk WFP may be the result of greater suppression of
seedlings by soybeans in the row than in the middle.
The data for standing biomass in the row and middles are presented
in Figures 4 and 5, respectively. The trend for standing biomass was similar to density data. This indicates that density was the major determining factor for standing biomass. Although there were some apparent differences in plant weight data (not presented), the trends were confounded between wild poinsettia density and time of 46
emergence relative to soybeans so that meaningful interpretations
were not obvious.
The infestation of wild poinsettia reduced soybean yields in both
years (Figures 6 and 7). In 1982, yield of the 3 wk WFP for the EPD was significantly lower relative to the remaining removal dates
(Figure 6 ). The yield of the 3 wk WFP at the LPD was not less than
the remainder of the removal dates. This indicates that sufficient
reinfestation occurred after the 3 wk WFP for the EPD to cause yield
reduction, but not for the LPD.
In 1983, severe herbicide injury resulted from the applications
of dinoseb to the 6 wk, 9 wk, and continous WFP. This accounted for
general yield reductions for those treatments and restricted
interpretation of the data for 0 and 3 wk WFP (Figure 7). At the 3 wk WFP, which was not injured by dinoseb, reinfestation in the EPD again resulted in a significant reduction in yield relative to the
LPD as in the 1982 data.
The maximum density determined in this study was equivalent to only 1 0 % of the base seed sample for the seed depletion study.
Since the areas had similar plant populations the year before and were managed similarly prior to establishing the experiments, the seed banks should have been about the same. This indicates that 10% or less of the seed bank could cause a serious weed problem in the crop. This maximum density is equivalent to approximately 16% of the total seedlings which emerged in the seed depletion study.
Results from these studies indicated that only 0 to 5% of the wild poinsettia seed bank persisted for more than one year after seeds are produced. Seeds buried 200 mm or greater contributed very 47
little to seedling emergence, however persistence of viable seed was
only slightly greater than at shallower depths. This contradicts
data presented by Bannon et al. (1) which indicated no loss of
viability in seeds buried 300 mm for 9 months in an Olivier silt
loam (fine-silty, mixed, thermic Aquic Fragiudalfs) also near Baton
Rouge. Difference in soil type could have been responsible for the
difference. The seed bank persistence was less than that reported
for other weeds (12). The planting date for soybeans in fields
infested with wild poinsettia could have some effect on the length
of weed control after planting needed to prevent reinfestation and
yield reductions. Approximately 3 and 6 wks of weed control would
be required to prevent reinfestation and yield reductions for
soybeans planted late (June 10) and early (May 1), respectively.
However, if an ineffective control program was used following each
planting date, more weeds might result from the LPD because of
greater emergence shortly after planting.
The low percentage of seed survival may be misleading in terms of practical wild poinsettia management. The base population of seeds
in the seed depletion study was equivalent to approximately 25 X 10^ 4 seeds per hectare (10 m ). If even 1% of such a high population became established in a crop, serious interference could result (7,
17). These studies indicate that intensive weed control or an
effective rotation crop should result in a decline of the population
in severely infested fields. However, if weed control practices were relaxed, and crop management were conducive to wild poinsettia growth, the population could be expected to increase rapidly from 48
either a low residual population or by dispersal from adjacent infested areas.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the partial financial support by the Louisiana Soybean Promotion Board. They also wish to thank
J. W. Shrefler, Paulette Johnsey, D. F. Goyer, L. L. Lyons and N. E.
Seger for their technical assistance. LITERATURE CITED
1. Bannon, J.S., J.B. Baker, and R.L. Rogers. 1978. Germination
of wild poinsettia (Euphorbia heterophylla). Weed Sci. 26:
221-225.
2. Barrentine, W.L. 1974. Common cocklebur competition in
soybeans. Weed Sci. 46: 129-140.
3. Dawson, J.H. and V.F. Bruns. 1975. Longevity of
barnyardgrass, green foxtail, and yellow foxtail seeds in soil.
Weed Sci. 23: 437-440.
4. Gebhardt, M.R. 1981. Cultural and chemical weed control
systems in soybeans (Glycine max). Weed Sci. 29: 133-138.
5. Gebhardt, M.R. 1981. Preemergence herbicides and cultivations
for soybeans (Glycine max) . Weed Sci. 29: 165-168.
6 . Gray, J. 1959. Soybean research in Louisiana. Soybean Dig.
19(9): 16-18.
7. Harger, T.R. and P.R. Nester. 1980. Wild poinsettia: A major
soybean weed. La. Agric. 23(3): 4-5 and 7.
8 . Harper, J.L. 1957. The ecological significance of dormancy
and its importance in weed control. Proc. 4th Int. Conf.
Prot., Hamburg, 415-420.
9. Hartwig, E.E. 1973. Varietal development. Pages 187-210 in
B.E. Caldwell, ed., Soybeans: Improvement, Production, and
Uses. Am. Soc. of Agron., Inc., Madison, WI.
49 10. Jenson, H.A. 1969. Content of buried seeds in arable soil in
Denmark and its relation to the weed population. Dansk bot.
Ark. 27(2): 1-56.
11. Kivilaan, A. and R.S. Bandurski. 1973. The ninety-year
period for Dr. Beal's seed viability experiment. Am. J. Bot.
60: 140-145.
12. Kropac, Z. 1966. Estimation of weed seeds in arable soil.
Pedobiologia 6 : 105-128.
13. Lindenbein, W. 1965. Tetrazolium testing. Proc. Int. Seed
Test. Assoc. 30: 89-97.
14. Lewis, J. 1973. Longevity of crops and weed seeds: survival
after 20 years in soil. Weed Res. 13: 179-191.
15. McWhorter, C.G. and W.L. Barrentine. 1975. Cocklebur control
in soybeans as affected by cultivars, seedling rates, and
methods of weed control. Weed Sci. 23: 386-389.
16. Murphy, T.R. and B.J. Gossett. 1981. Influence of shading by
soybeans (Glycine max) on weed suppression. Weed Sci. 29:
610-615.
17. Nester, P.R., T.R. Harger, and L.L. McCormick. 1979. Weed
watch - Wild poinsettia. Weeds Today 10(2): 24-25.
18. Peters, I.J., M.R. Gebhardt, and J.F. Stritzki. 1965.
Interrelations of row spacing, cultivations, and herbicides for
weed control in soybeans. Weeds 13: 285-289.
19. Roberts, H.A. 1962. Studies on the weeds of vegetable crops.
II. Effect of six years of cropping on the weed seeds in the
soil. J. Ecol. 50: 803-813. 51
20. Roberts, H.A. 1963. Studies on the weeds of vegetable crops.
III. Effect on different primary cultivations on the weed
seeds in the soil. J. Ecol. 51: 83-95.
21. Roberts, H.A. and P.A. Dawkins. 1967. Effects of cultivation
on the numbers of viable weed seeds in soil. Weed Res. 7:
290-301.
22. Roberts, H.A. and P.M. Feast. 1972. Fate of
seeds of some annual weeds in different depths of cultivated
and undisturbed soil. Weed Res. 12: 316-324.
23. Roberts, H.A. and R.T. Hewson. 1971. Herbicide performance
and soil surface conditions. Weed Res. 11: 69-73.
24. Roberts, H.A. and M.E. Ricketts. 1979. Quantitative
relationships between the weed flora after cultivation and the
seed population in the soil. Weed Res. 19: 269-275,
25. Schafer, D.E. and D.O. Chilcote. 1970. Factors influencing
persistence and depletion in buried seed populations. II.
The effects of soil temperature and moisture. Crop Sci. 10:
342-245.
26. Sokal, R.R. and F.J. Rohlf. 1981. Biometry, 2ed., W. H.
Freeman and Co., San Franciso. 859pp.
27. Thurlow, D.L. and G.A. Buchanan. 1972. Competition of
sicklepod with soybeans. Weed Sci. 20: 379-384.
28. Toole, E.H. and E. Brown. 1946. Final results of the Duvel
buried seed experiments. J. Agric. Res. 72: 201-210.
29. Wilson, H.P. and R.H. Cole. 1966. Morningglory competition in
soybeans. Weeds 14: 49-51. Table 1. Wild poinsettia seedling emergence during 1982 from seed buried in October 1981 as affected by burial depth.
Seedling Emergence
Burial Depth April May May June June July Total
2 10 20 4 22 9
______(7)aV'° / ______
10 0 3 0 <1 1 1 4
50 52 2 23 3 2 0 81
100 <1 1 22 5 2 <1 30
2 00 <1 0 <1 0 0 <1 1
LSD at P = 0.05 6 2 6 2 1 N.S. 8
Each number is the mean of 8 replications of 100 wild poinsettia seeds buried. Table 2 . Wild poinsettia seedling emergence during 1983 from seed buried in October of 1982 as affected by burial depth.
Seedling Emergence
Burial Depth May June June June July July Aug. Total
27 3 10 16 5 20 9
V'°(°/)a / ______--
10 5 0 4 <1 6 1 <1 15
50 26 4 16 1 13 7 0 66
100 5 <1 2 0 3 2 <1 12
200 0 0 <1 0 0 0 0 <1
LSD at P = 0.05 10 N.S. 9 N.S. 9 5 N.S. 20
Each number is the mean of 4 replications of 100 wild poinsettia seeds buried. 54
Table 3 . Average maximum and minimum monthly air temperature for
February through July in 1982 and 1983.
Year
Month 1982 1983
Max. Min. Max. Min.
(C)
February 17 5 16 6
March 21 12 20 7
April 24 14 23 11
May 29 18 28 17
June 33 21 30 19
July 34 22 33 22 55
Table 4 . Viability of wild poinsettia seed recovered after one or
two years of burial at four depths.
After 1 yr After 2 yr After 1 yr
1981 burial 1981 burial 1982 burial
Burial
Depths Rec. Germ. +TTC Rec. Germ. +TTC Rec . Germ. +TTC
_ f 7 ' ! ^ ______\'°) ————— a o V 10 3 0 0 4 0 0 0
50 1 0 0 0 0 0 0 0 0
100 <1 0 0 0 0 0 0 0 0
200 3 1 0 0 0 0 8 4 1
LSD at P=0.05 N.S. N.S. N.S. 3 N.S. N.S. 5 2 N.S.
liability was determined by germination, followed by TTC test of
firm seed which did not germinate.
^Percent based on 4 replications of 100 seeds buried at each depth.
CA total of 1 seed from all replications gave a positive test to
TTC. Table 5. Emergence of an agricultural seed bank of wild poinsettia as affected by cultivation over a two year period.
1982 1983 1982&1983
May June July August July July Overall
Cultivation regime3 31 23 9 6 Total 5 20 Total Total
None 817 697 23 1 1537 0 1 1 1538
1X-E 546 747 29 1 1322 1 0 1 1323
1X-M 753 689 32 2 1476 0 0 0 1476
2X-E.M 657 777 28 2 1464 0 2 2 1466
2X-M.L 790 733 22 2 1547 1 0 1 1548
3X-E,M,L 598 755 28 3 1383 0 0 0 1383
LSD at P = 0.05 N.S. N.S. N.S. N.S. N.S. N.S.N.S. N.S. N.S.
Means = 694 733 27 2 1455 0 1 1 1456
Cultivation was performed with a power rotary tiller operated to a depth of 60 mm. Cultivation was performed once (IX), twice (2X) or three times (3X) on the following dates: E - 5/10/82 and
4/25/83; M - 6/1/82 and 6/3/83; and L - 6/24/82 and 7/5/83. Table 6. Number of viable wild poinsettia seeds in the 0 to 60 mm depth of soil as affected by different cultivation regimes and sampling dates.
Base Sample-May '82 Residual Sample-October ''82
Cultivation regime3 Seeds/m2 Germ. +TTC Seeds/m2 Germ. +TTC
----- (%)C ----- (%)c ---
None 1770 79 8 5 0 50
1X-E 2091 85 7 0 0 0
IX-M 1700 88 6 7 0 0
2X-E.M 1831 88 5 7 0 0
2X-M.L 1751 89 8 5 100 0
3X-E.M.L 2105 90 6 2 100 0
LSD at P = 0.05 N.S. N.S. N.S. N.S. N.S. N.S.
Means = 1875 87 7 4b
Cultivation was performed the same as described in Table 6.
bTotal of 11 seeds were recovered, c Calculated as percent of recovered seed. Table 7 . Number of viable wild poinsettia seeds in the 60 to 120 mm depth of soil as affected by different cultivation regimes and sampling dates.
Residual sample
Base sample-May '82 October '82
Cultivation regime3 Seeds/m2 Germ. +TTC Seeds/m2
------(%) __
None 480 83 5 0
1X-E 523 80 6 0
1X-M 702 69 6 0
2X-E.M 428 78 5 0
2X-M,L 669 80 13 0
3X-E,M,L 824 82 4 0
LSD at P = 0.05 N.S. N.S. N.S. N.S.
Means = 604 79 7 0
Cultivation was performed the same as described in Table 6 . 59
Figure 1. Daily precipitation and dates of major emergence flushes of wild poinsettia from the buried seed study for 1982 and 1983, (a)
Numbers inside circles represents the percent of total seedling emergence during the season that was counted on the indicated date.
Figure 2 . Wild poinsettia density in the row as affected by planting dates (E = early, L = late), post-planting cultivations (IX
= once, 2X = twice), and weed-free period taken at harvest (October
28, 1982 and October 6 , 1983). An asterik above the bar indicates a significant difference between the cultivation regimes. Bars subtended by different letters indicate a significant difference of the groups above the bar when tested together. Differences determined by the Mann-Whitney U-Test at P. = 0.05. Each bar represents the mean of eight observations.
Figure 3. Wild poinsettia density in the middles as affected by planting dates (E = early, L = late), post-planting cultivations (IX
= once, 2X = twice), and weed-free period taken at harvest (October
28, 1982 and October 6 , 1983). An asterik above the bar indicates a significant difference between the cultivation regimes. Bars subtended by different letters indicate a significant difference of the groups above the bar when tested together. Differences determined by the Mann-Whitney U-Test at P. = 0.05. Each bar represents the mean of eight observations. Figure 4 . Standing biomass in the row as affected by planting dates
(E = early, L = late), post-planting cultivations (IX = once, 2X =
twice), and weed-free period taken at harvest (October 28, 1982 and
October 6 , 1983). An asterik above the bar indicates a significant
difference between the cultivation regimes. Bars subtended by
different letters indicate a significant difference of the groups
above the bar when tested together. Differences determined by the
Mann-Whitney U-Test at P. = 0.05. Each bar represents the mean of
eight observations.
Figure 5 . Standing biomass in the middle as affected by planting dates (E = early, L = late), post-planting cultivations (IX = once,
2X = twice), and weed-free period taken at harvest (October 28, 1982 and October 6 , 1983). An asterik above the bar indicates a significant difference between the cultivation regimes. Bars subtended by different letters indicate a significant difference of the groups above the bar when tested together. Differences determined by the Mann-Whitney U-Test at P. =0.05. Each bar represents the mean of eight observations.
Figure 6 . Yield in 1982 as affected by planting dates (EPD = early planting date and LPD = late planting date) and weed-free period.
Each bar represents the mean of eight observations.
Figure 7 . Yield in 1983 as affected by planting dates (EPD = early planting date and LPD = late planting date) and weed-free period.
Each bar represents the mean of eight observations. PRECIPIT ATION(cm) 0 3 4 4 1 0 3 2 1 2 6.6 APRIL
8.6 6.6 MAY f JUNE 7.0 JULY
17.4 93 1982 1983 61 DENSITY (plants/m2 ) 200 220 0 4 2 0 4 20 0 6 0 s ■ S ■ 0 ■ ■v ■s o ■ ■v \ ■ s s ns ns ns b c b a 0
EK WEED-FREE WEEKS 3
*> > * ■ _ s ns ns de d 6
2x 2x 1x 1 ___ X
62 DENSITY (plants/m2 ) 120 110 100 20 40 30 0 1 0 - - - - ' ' A / A ■ > ■ V ■S a 0 EK WEED-FREE WEEKS
JL b .1 JL Jt c a 3
■■I E ■■I ■■ E / / / /
c ■ S\ s ns ns c d L L 6
2x 2x 1x 1x
s ns ns 9 63 STANDING BIOMASS (g/m 2 ) 1000 1 1200
0 0 4 0 0 5 0 0 3 200 100 100 0
as N ■ C ■ \ ■ O ■ v ■ v ■ \ ■ k \ s ns ns b a s EK WEED-FREE WEEKS
^ a 0 ■ o ■ c ■ ns c
____ V' V ■ s ns ns df e _____ 2x 2x 1x 1x
g h dg 64 STANDING BIOMASS (g/m2 ) 1 1000 1200
8 0 0 - 0 0 8 100 200 - 0 0 9 3 0 0 - 0 0 3 - 0 0 7 100 0 ------/ / /
/
m N ■ JL a v 0 I
JL bd EK WEED-FREE WEEKS JL c L 3
JL d ■■■■I E > ■ iS 5 ns e ^ 6
ns fg 2x 2x 1x 1x ns 9 ns h 65 YIELD (Kg/ha) 40 - 2400 - 2600 80 - 2800 00 - 3000 2200 2000 1000 - 0 0 8 1 400 - 400 - 600 800 - 800 0 0 2 0 - - - - -
LSD P=0.05 EPD EK WEED-FREE WEEKS 3
6 LPD
9 Cont. 66 67
3200
3000
2800
2600
2400 LSDp=0>05 2200
2000
1800
1600
1400
1200
1000
800
200
0
0 3 6 9 Cont.
WEEKS WEED-FREE LITERATURE CITED
1. Alex, J. F. 1980. Emergence from buried seed and germination
of exhumed seed of fall panicum. Can. J. Plant Sci. 60:
635-642.
2. Alkamper, J. 1976. Influence of weed infestation on effect of
fertilizer dressings. Pflanzenschutz Nachrichten 29: 191-235.
3. Aspinall, D. and F. L. Milthorpe. 1959. An analysis of
competition between barley and white persicaria. Ann. Appl.
Biol. 47: 156-172.
4. Bannon, J. S., J. B. Baker, T. R. Harger, and R. L. Rogers.
1976. Weed watch. Weeds Today 8(1): 12.
5. Bannon, J. S., J. B. Baker, and R. L. Rogers. 1978.
Germination of wild poinsettia (Euphorbia heterophylla). Weed
Sci. 26: 221-225.
6 . Bannon, J. S., R. L. Rogers, J. L. Killmer, and P. R. Vidrine.
1975. Controlling wild poinsettia in soybeans. Abstr. Proc.
South Weed Sci. Soc. 28: 50.
7. Banting, J. D. 1966. Studies on the persistence of Avena
fatua. Can. J. Plant Sci. 46: 129-140.
8 . Barrentine, W. L. 1974. Common cocklebur competition in
soybeans. Weed Sci. 22: 600-603.
68 9. Bauer, A., R. A. Young, and J. L. Ozbun. 1965. Effects of
moisture and fertilizer on yields of spring wheat and barley.
Agron. J. 57: 354-356.
10. Biswas, P. K . , P.D. Bell, J.L. Crayton, and K.B. Paul. 1975.
Germination behavior of Florida pusley seeds. I. Effects of
storage, light, temperature and planting depths on germination.
Weed Sci. 23: 400-403.
11. Bleasdale, J. K. A. 1960. Studies on plant competition, pp.
133-142. in J. L. Harper, ed., The Biology of Weeds. Blackwell
Sci. Publ., Oxford, England.
12. Brecke, B. J. and W. B. Duke. 1980. Dormancy, germination, and
emergence characteristics of fall panicum (Panicum
dichotomiflorum) seed. Weed Sci. 28: 683-685.
13. Brenchley, W. E. and K. Warington. 1936. The weed seed
population of arable soil. III. The reestablishment of weed
species after reduction by fallowing. J. Ecol. 24: 479-501.
14. Buchanan, G. A. and E. R. Burns. 1970. Influence of weed
competition on cotton. Weed Sci. 18: 149-154.
15. Buchanan, G. A., R. H. Crowley, and R. D. McLoughlin. 1977.
Competition of prickly sida with cotton. Weed Sci. 25: 106-110.
16. Buchanan, G. A., E. W. Hauser, W. J. Ethredge, and S. R. Cecil.
1976. Competition of Florida beggarweed and sicklepod with
peanuts. II. Effects of cultivation, weeds, and SADH. Weed
Sci. 24: 29-39.
17. Burnside, 0. C. and G. A. Wicks. 1969. Influence of weed
competition on sorghum growth. Weed Sci. 17: 332-334. 18. Carter, 0. G. 1974. Detailed analysis of the effect of
different planting dates on seven soybean varieties. Iowa State
J. Res. 48: 291-310.
19. Caviness, C. E. 1966. Spacing studies with Lee soybeans.
Arkansas Agric. Exp. Stn. Bull. 713.
20. Chancellor, R. J. 1964. The depth of weed seed germination in
the field. Proc. 7th Br. Weed Control Conf., 607-613.
21. Chepil, W. S. 1946. Germination of weed seeds. II. The
influence of tilling treatments on germination. Sci. Agric. 26:
347-357.
22. Clements, F. E. 1907.Plant Physiology and Ecology. H. Hott
and Co., N.Y. pp. 251-269.
23. Clements, F. E., J. E. Weaver, and H. C. Hanson. 1929. Plant
competition - an analysis of community function. Publ. No. 398.
Carnegie Institute, Wash., D.C. 340 pp.
24. Darlington, H. T. 1931. The 50-year period for Dr. Beal's seed
viability experiment. Am. J. Bot. 18: 262-265.
25. Davis, G., E. Voll, and H. Lorenzi. 1978. Control of annual
weeds in soybeans of southern Brazil. Abstr. Proc. South. Weed
Sci. Soc. 31: 96.
26. Dawson, J. H. and V. F. Bruns. 1975. Longevity of
barnyardgrass, green foxtail, and yellow foxtail seeds in soil.
Weed Sci. 23: 437-440.
27. Donald, C. M. 1963. Competition among crop and pasture plants.
Advances in Agron. 15: 1-118. Acad. Press, N.Y. 28. Egley, G. H. and J. M Chandler. 1978. Germination and
viability of weed seeds after 2.5 years in a 50-year buried seed
study. Weed Sci. 26: 230-239.
29. Fogelfors, H. 1972. The development of some weed species under
different conditions of light and their competition ability in
barley stands, in Weeds and Weed Control, 13th Swed. Weed
Conf., Uppsala, part 1: F4-F5.
30. Gebhardt, M. R. 1981. Cultural and chemical weed control
systems in soybeans (Glycine max). Weed Sci. 29: 133-138.
31. Gebhardt, M. R. 1981. Preemergence herbicides and cultivations
for soybeans (Glycine max) . Weed Sci. 29: 165-168.
32. Gomes, L. F., J. M. Chandler, and C. E. Vaughan. 1978. Aspects
of germination, emergence, and seed production of three Ipomoea
taxa. Weed Sci. 26: 245-248.
33. Gray, J. 1959. Soybean research in Louisiana. Soybean Dig.
19(9): 16-18.
34. Harger, T. R. and P. R. Nester. 1980. Wild poinsettia: A
major soybean weed. La. Agric. 23(3): 4-5 and 7.
35. Harper, J. L. 1957. The ecological significance of dormancy
and its importance in weed control. Proc. 4th Int. Conf. Prot.,
Hamburg, 415-420.
36. Harper, J. L. 1977. Population biology of plants. Academic
Press, New York. 892 pp.
37. Hartwig, E. E. 1973. Varietal development. Pages 187-210 in
B. E. Caldwell, ed., Soybeans: Improvement, Production, and
Uses. Am. Soc. of Agron., Inc., Madison, WI. 38. Hawkins, H. S. and J. N. Black. 1958. Competition between
wheat and three cornered jack (Emex australis Steinh.). Aust.
Inst, of Agric. Sci. J. 24: 45-50.
39. Hill, L. V. and P. W. Santelmann. 1969. Competitive effects of
annual weeds on Spanish peanuts. Weed Sci. 17: 1-2.
40. Hinesly, T. D., E. L. Knake, and R. D. Sief. 1967. Herbicide
versus cultivation for corn with two methods of seedbed
preparation. Agron. J. 59: 509-512.
41. Jenson, H. A. 1969. Content of buried seeds in arable soil in
Denmark and its relation to the weed population. Dansk bot.
Ark. 27(2): 1-56.
42. Keay, R. W. J., editor. 1973. Flora of west tropical Africa,
Vol. I. Crown Agents for Overseas Governments and
Administration. London, pp. 297-828.
43. Kivilaan, A. and R. S. Bandurski. 1973. The ninety-year period
for Dr. Beal's seed viability experiment. Am. J. Bot. 60:
140-145.
44. Klingman, G. C. 1961. Weed control: as a science. John Wiley
and Sons Inc., New York. 421 pp.
45. Knake, E. L. and F. W. Slife. 1962. Competition of Setaria
faberii with corn and soybeans. Weeds 10: 26-29.
46. Kropac, Z. 1966. Estimation of weed seeds in arable soil.
Pedobiologia 6 : 105-128.
47. Lewis, J. 1973. Longevity of crops and weed seeds: survival
after 20 years in soil. Weed Res. 13: 179-191.
48. Loomis, W. E. 1958. Basic studies in botany, ecology, and
plant physiology. Proc. North Cent. Weed Cont. Conf. 15: 81. 73
49. Lueschen, W. E. and R. N. Anderson. 1980. Longevity of
velvetleaf (Abutilon theophrasti) seeds in soil under
agricultural practices. Weed Sci. 28: 341-346.
50. Mather, K. 1961. Competition and cooperation. Mechanisms in
Biological Competition. Soc. for Expt. Biol. Symp. IV.
Academic Press, N.Y. 15: 264-281.
51. McWhorter, C. G. and W. L. Barrentine. 1975. Cocklebur control
in soybeans as affected by cultivars, seeding rates, and methods
of weed control. Weed Sci. 23: 386-389.
52. Moolani, M. K . , E. L. Knake, and F. W. Slife. 1964.
Competition of smooth pigweed with corn and soybeans. Weeds 12:
126-128.
53. Murphy, T. R. and B. J. Gossett. 1981. Influence of shading by
soybeans (Glycine max) on weed suppression. Weed Sci. 29:
610-615.
54. Nakoneshny, W. and G. Friesen. 1961. The influence of a
commercial fertilizer treatment on weed competition in spring
sown wheat. Can. J. Plant Sci. 41: 231-238.
55. Nelson, D. C. and R. E. Nylund. 1962. Competition between peas
grown for processing and weeds. Weeds 10: 224-228.
56. Nester, P. R., T. R. Harger, and L. L. McCormick. 1979. Weed
watch - Wild poinsettia. Weeds Today 10(2): 24-25.
57. Nieto, J., M. A. Brando, and J. T. Gonzalez. 1968. Critical
periods of the crops growth cycle for competition from weeds.
PANS (c) 14: 159-166. 74
58. Oliver, L. R. 1979. Influence of soybean (Glycine max)
planting date on velvetleaf (Abutilon theophrasti) competition.
Weed Sci. 27: 183-188.
59. Pavlychenko, T. K. 1937. Quantitative study of the entire root
systems of weeds and crop plants under field conditions.
Ecology 18: 62-79.
60. Pendleton, J. W., R. L. Bernard, and H. Hadley. 1960. Grow
soybeans in narrow rows. 111. Res. 2: 3-4.
61. Peters, E. J., F. S. Davis, D. L. Klingman and R. E. Larson.
1961. Interrelations of cultivations, herbicides, and methods
of application for weed control in soybeans. Weeds 9: 639-645.
62. Peters, E. J., M. R. Gebhardt, and J. F. Stritzki. 1965.
Interrelations of row spacing, cultivations, and herbicides for
weed control in soybeans. Weeds 13: 285-289.
63. Roberts, H. A. 1962. Studies on the weeds of vegetable crops.
II. Effect of six years of cropping on the weed seeds in the
soil. J. Ecol. 50: 803-813.
64. Roberts, H. A. 1963. Studies on the weeds of vegetable crops.
III. Effect of different primary cultivations on the weed seeds
in the soil. J. Ecol. 51: 83-95.
65. Roberts, H. A. 1972 Dormancy: A factor affecting seed
survival in the soil. Pages 321-359 in E. H. Roberts, ed.,
Viability of seeds. Syracuse University Press, Syracuse, N.Y.
6 6 . Roberts, H. A. and P. A. Dawkins. 1967. Effects of cultivation
on the numbers of viable weed seeds in soil. Weed Res. 7:
290-301. 67. Roberts, H. A. and P. M. Feast. 1972. Fate of seeds of some
annual weeds in different depths of cultivated and undisturbed
soil. Weed Res. 12: 316-324.
6 8 . Roberts, H. A. and P. M. Feast. 1973. Emergence and longevity
of seeds of annual weeds in cultivated and undisturbed soils.
J. Appl. Ecol. 10: 133-143.
69. Roberts, H. A. and R. T. Hewson. 1971. Herbicide performance
and soil surface conditions. Weed Res. 11: 69-73.
70. Roberts, H. A. and M. E. Ricketts. 1979. Quantitative
relationships between the weed flora after cultivation and the
seed population in the soil. Weed Res. 19: 269-275.
71. Russell, W. J., W. R. Fehr, and R. L. Mitchell. 1971. Effects
of row cultivation on growth and yield of soybeans. Agron. J.
63: 772-774.
72. Sagar, G. R. 1968. Factors affecting the outcome of
competition between crops and weeds. Proc. 9th Brit. Weed Cont.
Conf. pp. 1157-1162.
73. Sanders, Dearl. 1983. Weed survey - Southern states. South.
Weed Sci. Soc. Res. Rep. 36: 168, 180-181.
74. Schafer, D. E. and D. 0. Chilcote. 1970. Factors influencing
persistence and depletion in buried seed populations. II. The
effects of soil temperature and moisture. Crop Sci. 10:
342-345.
75. Smith, R. L. 1968. Effect of planting date and row width on
yield of soybeans. Soil Crop Sci. Soc. Fla. 28: 130-133.
76. Smith, T. J., H. M. Camper, M. T. Carter, G. D. Jones, and M. W.
Alexander. 1961. Soybean performance in Virginia as affected by variety and planting date. Virginia Agric. Exp. Stn. Bull.
526. 30 pp.
77. Solano, F., J. W. Schrader, and H. D. Coble. 1974. Germination
and emergence of spurred anoda. Weed Sci. 22: 353-354.
78. Standifer, L. C. 1980. A technique for estimating weed seed
populations in the soil. Weed Sci. 28: 134-139.
79. Staniforth, D. W. 1958. Soybean-foxtail competition under
varying soil moisture conditions. Agron. J. 50: 12-15.
80. Staniforth, D. W. 1965. Competitive effects of three foxtail
species on soybeans. Weeds 13: 191-192.
81. Stoller, E. W. and L. M. Wax. 1973. Periodicity of germination
and emergence of some annual weeds. Weed Sci. 21: 574-580.
82. Stoller, E. W. and L. M. Wax. 1974. Dormancy changes and fate
of some annual weed seeds in the soil. Weed Sci. 22: 151-155.
83. Suomela, H. and J. Poatela. 1962. The influence of irrigation,
fertilizing and MCPA on the competition between spring cereals
and weeds. Weed Res. 2: 90-99.
84. Taylorson, R. B. 1970. Changes in dormancy and viability of
weed seeds in soils. Weed Sci. 18: 265-269.
85. Taylorson, R. B. 1972. Phytochrome controlled changes in
dormancy and germination of buried weed seeds. Weed Sci. 20:
417-422.
8 6 . Thurlow, D. L. and G. A. Buchanan. 1972. Competition of
sicklepod with soybeans. Weed Sci. 20: 379-384.
87. Toole, E. H. and E. Brown. 1946. Final results of the Duvel
buried seed experiments. J. Agric. Res. 72: 201-210. 8 8 . Vengris, J., W. G. Colby, and M. Drake. 1955. Plant nutrient
competition between weeds and corn. Agron. J. 47: 213-216.
89. Vidrine, P. R . , J. L. Killmer, and R. L. Rogers. 1974.
Controlling wild poinsettia in soybeans. Abstr. Proc. South.
Weed Sci. Soc. 27: 47.
90. Waldron, L. R. 1904. Vitality and growth of buried weed seed.
N. Dak. Agric. Exp. Sta. Bull. 62: 439-457.
91. Williams, C., J. J. Daigle, L. Mason, and D. L. Robinson. 1972.
Response of three soybean varieties to varying plant population
density and row spacing. Louisiana Agric. Exp. Stn., Dep.
Agron. Rep. Proj. p. 176-183.
92. Williams, C., L. Mason, and B. E. Newman. 1970. Response of
four soybean varieties to varying plant population density and
row spacing. Louisiana Agric. Exp. Stn., Dep. Agron. Rep. Proj.
p. 135-143.
93. Williams, C., and R. B. M. Noor. 1973. Effect of date of
planting and row spacing on yield and other agronomic
characteristics of three varieites of soybean. Louisiana Agric.
Exp. Stn., Dep. Agron. Rep. Proj. p. 176-184.
94. Wilson, A. K. 1981. Euphorbia heterophylla: A review of
distribution, importance and control. Tropical Pest Management
27(1): 32-38.
95. Wilson, H. P. and R. H. Cole. 1966. Morningglory competition
in soybeans. Weeds 14: 49-51.
96. Witts, K. J. 1957. Effect of competition (Agrostis gigantea)
on response of wheat to nitrogenous top dressing. Rept.
Rothamsted Expt. Stn., Harpenden, Herts., England, pp. 93-94. APPENDIX I
78 Appendix Table 1-1. Dry weight of wild poinsettia plants remaining in the soybean drill (150 mm on each side of the drill) after various weed-free maintenance periods in 1982 taken at harvest.
EPD - April 29 LPD - June 14
Cultivation3 Cultivation
Weeks of w e e d - f r e e ------Maintenance^ IX 2X IX 2X
------(g/plant)------
0 8.4 19.2 5.6 4.7
3 8.7 17.6 3.7 0.8
6 3.0 2.0 6.1 0.5
9 0 0 0 0
Continous 0 0 0 0
LSD 0.05 6,3 £ Cultivation was performed with a Lilliston R rolling cultivator.
IX cultivation performed at 3 wk interval only, whereas 2X cultivation was performed at 3 and 6 wk intervals.
^Weeks of weed-free maintenance before wild poinsettia was allowed to reinfest. 80
Appendix Table 1-2. Dry weight of wild poinsettia plants remaining
in the soybean drill (150 mm on each side of the drill) after various weed-free maintenance periods in 1983 taken at harvest.
EPD - April 28 LPD - June 7
Cultivation Cultivation
Weeks of weed-free
Maintenance^ IX 2X IX 2X
(g/plant)
0 7.8 7.9 4.2 6.1
3 9.1 10.5 3.7 2.3
6 10.4 7.0 3.0 2.3
9 5.8 5.7 0 0
Continous 0 0 0 0
LSD 0 0 5 = 3.9
Cultivation was performed with a Lilliston R rolling cultivator.
IX cultivation performed at 3 wk interval only, whereas 2X cultivation was performed at 3 and 6 wk intervals.
^Weeks of weed-free maintenance before wild poinsettia was allowed to reinfest. 81
Appendix Table 1-3. Dry weight of wild poinsettia plants remaining in the middles after various weed-free maintenance periods in 1982, taken at harvest.
EPD - April 29 LPD - June 14
Cultivation3 Cultivation
Weeks of weed-free
Maintenance^3 IX 2X IX 2X
\§/ pXulluy
0 10.5 4.5 7.2 7.0
3 14.1 6 . 0 14.1 1.5
6 4.0 10.1 5.4 1.2
9 0 0 0 0
Continous 0 0 0 0
LSD0.05 5, 3 Cultivation was performed with a Lilliston R rolling cultivator.
IX cultivation performed at 3 wk interval only, whereas 2X cultivation was performed at 3 and 6 wk intervals.
^Weeks of weed-free maintenance before wild poinsettia was allowed to reinfest. 82
Appendix Table 1-4. Dry weight of wild poinsettia plants remaining
in the middles after various weed-free maintenance periods in 1983,
taken at harvest.
EPD - April 28 LPD - June 7
Cultivation Cultivation Weeks of weed-free
Maintenance*3 IX 2X IX 2X
V.g/pxanty ——
0 6.1 8. 2 4.8 4.6
3 6.5 9.2 9.0 0.3
6 1 2. 0 13.7 3.6 1.9
9 7.5 5.5 0 . 6 1.1
Continous 0 0 0 0
LSD0.05 “ 4,6 Cultivation was performed with a Lilliston R rolling cultivator.
IX cultivation performed at 3 wk interval only, whereas 2X cultivation was performed at 3 and 6 wk intervals.
^Weeks of weed-free maintenance before wild poinsettia was allowed to reinfest. APPENDIX II
83 84
Appendix Table II-l. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for wild poinsettia density in the row.
Comparisons Probability
EPD vs. LPD at 0 wk WFP * P. = 0 . 0 0 1
EPD vs. LPD at 3 wk WFP * P. = 0 . 0 0 1
EPD vs. LPD at 6 wk WFP * P. = 0.05
0 wk vs. 3 wk WFP at EPD * P. = 0.05
3 wk vs. 6 wk WFP at EPD * P. = 0.05
0 wk vs. 3 wk WFP at LPD * P. = 0 . 0 0 1
3 wk vs. 6 wk WFP at LPD N.S.
0 wk WFP (LPD) vs 6 wk WFP (EPD) N.S. 85
Appendix Table II-2. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for wild poinsettia density in the middle.
Comparisons Probability
EPD vs. LPD at 0 wk WFP * P. = 0 . 0 0 1
EPD vs. LPD at 3 wk WFP * P. = 0.001
EPD vs. LPD at 6 wk WFP * P. = 0 . 0 0 1
0 wk vs. 3 wk WFP at EPD N.S.
0 wk vs. 3 wk WFP at LPD * P. = 0.05
3 wk vs. 6 wk WFP at LPD N.S.
0 wk WFP (LPD) vs. 6 wk WFP (EPD) N.S.
0 wk plus 3 wk vs. 6 wk WFP at EPD * P. = 0 . 0 0 1 86
Appendix Table II-3. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for standing biomass in the row.
Comparisons Probability
EPD vs. LPD at 0 wk WFP * P. = 0.001
EPD vs. LPD at 3 wk WFP * P. = 0.001
EPD vs. LPD at 6 wk WFP * P. = 0.05
EPD vs. LPD at 9 wk WFP * P. = 0.001
0 wk vs. 3 wk WFP at EPD * P. = 0.05
3 wk vs. 6 wk WFP at EPD * P. = 0.001
6 wk vs. 9 wk WFP at EPD * P. » 0.05
0 wk vs. 3 wk WFP at LPD * P. = 0.001
3 wk vs. 6 wk WFP at LPD N.S.
6 wk vs. 9 wk WFP at LPD * P. = 0.001
0 wk WFP (LPD) vs. 3 wk WFP (EPD) * P. = 0.001
3 wk WFP (LPD) vs. 9 wk WFP (EPD) N.S.
6 wk WFP (LPD) vs. 9 wk WFP (EPD) N.S. 87
Appendix Table II-4. Comparisons tested and their levels of probability as determined by the Mann-Whitney U-Test for standing biomass in the middle.
Comparisons Probability
EPD vs. LPD at 0 wk WFP * P. = 0 . 0 0 1
EPD vs. LPD at 3 wk WFP * P. = 0 . 0 0 1
EPD vs. LPD at 6 wk WFP * P. = 0 . 0 0 1
EPD vs. LPD at 9 wk WFP * P. = 0.05
0 wk vs. 3 wk WFP at EPD * P. = 0 . 0 0 1
3 wk vs. 6 wk WFP at EPD * P. = 0 . 0 0 1
6 wk vs. 9 wk WFP at EPD * P. = 0 . 0 0 1
0 wk vs. 3 wk WFP at LPD N..S.
3 wk vs. 6 wk WFP at LPD * P. = 0.05
6 wk vs. 9 wk WFP at LPD * P. = 0.05
0 wk WFP (LPD) vs. 3 wk WFP (EPD) * P. = 0 . 0 0 1
3 wk WFP (LPD) vs. 6 wk WFP (EPD) * P. = 0.05
6 wk WFP (LPD) vs. 9 wk WFP (EPD) N..S. 88
VITA
Vernon B. Langston was born June 18, 1955 in Jackson,
Mississippi to Mr. and Mrs. Robert B. Langston, Jr. He received his primary and secondary education in Raymond, Mississippi and graduated from Raymond High School in May 1973.
In August 1973 he entered Hinds Jr. College at Raymond,
Mississippi, majoring in Agronomy, and transfered to Mississippi
State University in Starkville, Mississippi. He received his
Bachelor of Science degree in May 1977. In 1979, he graduated with a Master of Science degree in Weed Science from Mississippi State
University. The author accepted the position of Research Associate at the Red River Research Station in Bossier City, Louisiana, remaining there until December 31, 1980. In January 1981 the author accepted the position of Research Assistant in the Department of
Plant Pathology and Crop Physiology at Louisiana State University.
There he pursued a Doctor of Philosophy degree with a major in Weed
Science and a minor in Agronomy for which he is now a candidate. EXAMINATION AND THESIS REPORT
Candidate: Vernon B. Langston
Major Field: Plant Pathology
Title of Thesis: Behavior of Euphorbia Heterophylla Seed Bank
Approved:
Major Professor and fian
Dean of the Graduate chool
EXAMINING COMMITTEE:
/ S • f'CJ'
t
Date of Examination:
Nov. 23, 1983